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11 Column Types

MySQL supports a number of column types in several categories: numeric types, date and time types, and string (character) types. This chapter first gives an overview of these column types, and then provides a more detailed description of the properties of the types in each category, and a summary of the column type storage requirements. The overview is intentionally brief. The more detailed descriptions should be consulted for additional information about particular column types, such as the allowable formats in which you can specify values.

MySQL versions 4.1 and up support extensions for handing spatial data. Information about spatial types is provided in section 18 Spatial Extensions in MySQL.

Several of the column type descriptions use these conventions:

M

Indicates the maximum display width. The maximum legal display width is 255.

D

Applies to floating-point and fixed-point types and indicates the number of digits following the decimal point. The maximum possible value is 30, but should be no greater than M-2.

Square brackets (`[' and `]') indicate parts of type specifiers that are optional.

11.1 Column Type Overview

11.1.1 Overview of Numeric Types

A summary of the numeric column types follows. For additional information, see section 11.2 Numeric Types. Column storage requirements are given in section 11.5 Column Type Storage Requirements.

M indicates the maximum display width. The maximum legal display width is 255. Display width is unrelated to the storage size or range of values a type can contain, as described in section 11.2 Numeric Types.

If you specify ZEROFILL for a numeric column, MySQL automatically adds the UNSIGNED attribute to the column.

Warning: You should be aware that when you use subtraction between integer values where one is of type UNSIGNED, the result will be unsigned! See section 12.7 Cast Functions and Operators.

TINYINT[(M)] [UNSIGNED] [ZEROFILL]

A very small integer. The signed range is -128 to 127. The unsigned range is 0 to 255.

BIT

BOOL

BOOLEAN

These are synonyms for TINYINT(1). The BOOLEAN synonym was added in MySQL 4.1.0. A value of zero is considered false. Non-zero values are considered true. In the future, full boolean type handling will be introduced in accordance with standard SQL.

SMALLINT[(M)] [UNSIGNED] [ZEROFILL]

A small integer. The signed range is -32768 to 32767. The unsigned range is 0 to 65535.

MEDIUMINT[(M)] [UNSIGNED] [ZEROFILL]

A medium-size integer. The signed range is -8388608 to 8388607. The unsigned range is 0 to 16777215.

INT[(M)] [UNSIGNED] [ZEROFILL]

A normal-size integer. The signed range is -2147483648 to 2147483647. The unsigned range is 0 to 4294967295.

INTEGER[(M)] [UNSIGNED] [ZEROFILL]

This is a synonym for INT.

BIGINT[(M)] [UNSIGNED] [ZEROFILL]

A large integer. The signed range is -9223372036854775808 to 9223372036854775807. The unsigned range is 0 to 18446744073709551615. Some things you should be aware of with respect to BIGINT columns:

• All arithmetic is done using signed BIGINT or DOUBLE values, so you shouldn't use unsigned big integers larger than 9223372036854775807 (63 bits) except with bit functions! If you do that, some of the last digits in the result may be wrong because of rounding errors when converting a BIGINT value to a DOUBLE. MySQL 4.0 can handle BIGINT in the following cases:
  • When using integers to store big unsigned values in a BIGINT column.
  • In MIN(col_name) or MAX(col_name), where col_name refers to a BIGINT column.
  • When using operators (+, -, *, and so on) where both operands are integers.
• You can always store an exact integer value in a BIGINT column by storing it using a string. In this case, MySQL performs a string-to-number conversion that involves no intermediate double-precision representation.
• The -, +, and * operators will use BIGINT arithmetic when both operands are integer values! This means that if you multiply two big integers (or results from functions that return integers), you may get unexpected results when the result is larger than 9223372036854775807.

FLOAT(p) [UNSIGNED] [ZEROFILL]

A floating-point number. p represents the precision. It can be from 0 to 24 for a single-precision floating-point number and from 25 to 53 for a double-precision floating-point number. These types are like the FLOAT and DOUBLE types described immediately following. FLOAT(p) has the same range as the corresponding FLOAT and DOUBLE types, but the display width and number of decimals are undefined. As of MySQL 3.23, this is a true floating-point value. In earlier MySQL versions, FLOAT(p) always has two decimals. This syntax is provided for ODBC compatibility. Using FLOAT might give you some unexpected problems because all calculations in MySQL are done with double precision. See section A.5.7 Solving Problems with No Matching Rows.

FLOAT[(M,D)] [UNSIGNED] [ZEROFILL]

A small (single-precision) floating-point number. Allowable values are -3.402823466E+38 to -1.175494351E-38, 0, and 1.175494351E-38 to 3.402823466E+38. If UNSIGNED is specified, negative values are disallowed. M is the display width and D is the number of decimals. FLOAT without arguments or FLOAT(p) (where p is in the range from 0 to 24) stands for a single-precision floating-point number.

DOUBLE[(M,D)] [UNSIGNED] [ZEROFILL]

A normal-size (double-precision) floating-point number. Allowable values are -1.7976931348623157E+308 to -2.2250738585072014E-308, 0, and 2.2250738585072014E-308 to 1.7976931348623157E+308. If UNSIGNED is specified, negative values are disallowed. M is the display width and D is the number of decimals. DOUBLE without arguments or FLOAT(p) (where p is in the range from 25 to 53) stands for a double-precision floating-point number.

DOUBLE PRECISION[(M,D)] [UNSIGNED] [ZEROFILL]

REAL[(M,D)] [UNSIGNED] [ZEROFILL]

These are synonyms for DOUBLE. Exception: If the server SQL mode includes the REAL_AS_FLOAT option, REAL is a synonym for FLOAT rather than DOUBLE.

DECIMAL[(M[,D])] [UNSIGNED] [ZEROFILL]

An unpacked fixed-point number. Behaves like a CHAR column; ``unpacked'' means the number is stored as a string, using one character for each digit of the value. M is the total number of digits and D is the number of decimals. The decimal point and (for negative numbers) the `-' sign are not counted in M, although space for them is reserved. If D is 0, values have no decimal point or fractional part. The maximum range of DECIMAL values is the same as for DOUBLE, but the actual range for a given DECIMAL column may be constrained by the choice of M and D. If UNSIGNED is specified, negative values are disallowed. If D is omitted, the default is 0. If M is omitted, the default is 10. Prior to MySQL 3.23, the M argument must be large enough to include the space needed for the sign and the decimal point.

DEC[(M[,D])] [UNSIGNED] [ZEROFILL]

NUMERIC[(M[,D])] [UNSIGNED] [ZEROFILL]

FIXED[(M[,D])] [UNSIGNED] [ZEROFILL]

These are synonyms for DECIMAL. The FIXED synonym was added in MySQL 4.1.0 for compatibility with other servers.

11.1.2 Overview of Date and Time Types

A summary of the temporal column types follows. For additional information, see section 11.3 Date and Time Types. Column storage requirements are given in section 11.5 Column Type Storage Requirements.

DATE

A date. The supported range is '1000-01-01' to '9999-12-31'. MySQL displays DATE values in 'YYYY-MM-DD' format, but allows you to assign values to DATE columns using either strings or numbers.

DATETIME

A date and time combination. The supported range is '1000-01-01 00:00:00' to '9999-12-31 23:59:59'. MySQL displays DATETIME values in 'YYYY-MM-DD HH:MM:SS' format, but allows you to assign values to DATETIME columns using either strings or numbers.

TIMESTAMP[(M)]

A timestamp. The range is '1970-01-01 00:00:00' to partway through the year 2037. A TIMESTAMP column is useful for recording the date and time of an INSERT or UPDATE operation. The first TIMESTAMP column in a table is automatically set to the date and time of the most recent operation if you don't assign it a value yourself. You can also set any TIMESTAMP column to the current date and time by assigning it a NULL value. From MySQL 4.1 on, TIMESTAMP is returned as a string with the format 'YYYY-MM-DD HH:MM:SS'. If you want to obtain the value as a number, you should add +0 to the timestamp column. Different timestamp display widths are not supported. In MySQL 4.0 and earlier, TIMESTAMP values are displayed in YYYYMMDDHHMMSS, YYMMDDHHMMSS, YYYYMMDD, or YYMMDD format, depending on whether M is 14 (or missing), 12, 8, or 6, but allows you to assign values to TIMESTAMP columns using either strings or numbers. The M argument affects only how a TIMESTAMP column is displayed, not storage. Its values always are stored using four bytes each. From MySQL 4.0.12, the --new option can be used to make the server behave as in MySQL 4.1. Note that TIMESTAMP(M) columns where M is 8 or 14 are reported to be numbers, whereas other TIMESTAMP(M) columns are reported to be strings. This is just to ensure that you can reliably dump and restore the table with these types.

TIME

A time. The range is '-838:59:59' to '838:59:59'. MySQL displays TIME values in 'HH:MM:SS' format, but allows you to assign values to TIME columns using either strings or numbers.

YEAR[(2|4)]

A year in two-digit or four-digit format. The default is four-digit format. In four-digit format, the allowable values are 1901 to 2155, and 0000. In two-digit format, the allowable values are 70 to 69, representing years from 1970 to 2069. MySQL displays YEAR values in YYYY format, but allows you to assign values to YEAR columns using either strings or numbers. The YEAR type is unavailable prior to MySQL 3.22.

11.1.3 Overview of String Types

A summary of the string column types follows. For additional information, see section 11.4 String Types. Column storage requirements are given in section 11.5 Column Type Storage Requirements.

In some cases, MySQL may change a string column to a type different from that given in a CREATE TABLE or ALTER TABLE statement. See section 13.2.6.1 Silent Column Specification Changes.

A change that affects many string column types is that, as of MySQL 4.1, character column definitions can include a CHARACTER SET attribute to specify the character set and, optionally, a collation. This applies to CHAR, VARCHAR, the TEXT types, ENUM, and SET. For example:

CREATE TABLE t
(
    c1 CHAR(20) CHARACTER SET utf8,
    c2 CHAR(20) CHARACTER SET latin1 COLLATE latin1_bin
);

This table definition creates a column named c1 that has a character set of utf8 with the default collation for that character set, and a column named c2 that has a character set of latin1 and the binary collation for the character set. The binary collation is not case sensitive.

Character column sorting and comparison are based on the character set assigned to the column. Before MySQL 4.1, sorting and comparison are based on the collation of the server character set. For CHAR and VARCHAR columns, you can declare the column with the BINARY attribute to cause sorting and comparison to be case sensitive using the underlying character code values rather then a lexical ordering.

For more details, see section 10 Character Set Support.

Also as of 4.1, MySQL interprets length specifications in character column definitions in characters. (Earlier versions interpret them in bytes.)

[NATIONAL] CHAR(M) [BINARY | ASCII | UNICODE]

A fixed-length string that is always right-padded with spaces to the specified length when stored. M represents the column length. The range of M is 0 to 255 characters (1 to 255 prior to MySQL 3.23). Note: Trailing spaces are removed when CHAR values are retrieved. From MySQL 4.1.0, a CHAR column with a length specification greater than 255 is converted to the smallest TEXT type that can hold values of the given length. For example, CHAR(500) is converted to TEXT, and CHAR(200000) is converted to MEDIUMTEXT. This is a compatibility feature. However, this conversion causes the column to become a variable-length column, and also affects trailing-space removal. CHAR is shorthand for CHARACTER. NATIONAL CHAR (or its equivalent short form, NCHAR) is the standard SQL way to define that a CHAR column should use the default character set. This is the default in MySQL. As of MySQL 4.1.2, the BINARY attribute is shorthand for specifying the binary collation of the column character set. Before 4.1.2, BINARY attribute causes the column to be treated as a binary string. In either case, sorting and comparisons become case sensitive. From MySQL 4.1.0 on, the ASCII attribute can be specified. It assigns the latin1 character set to a CHAR column. From MySQL 4.1.1 on, the UNICODE attribute can be specified. It assigns the ucs2 character set to a CHAR column. MySQL allows you to create a column of type CHAR(0). This is mainly useful when you have to be compliant with some old applications that depend on the existence of a column but that do not actually use the value. This is also quite nice when you need a column that can take only two values: A CHAR(0) column that is not defined as NOT NULL occupies only one bit and can take only the values NULL and '' (the empty string).

CHAR

This is a synonym for CHAR(1).

[NATIONAL] VARCHAR(M) [BINARY]

A variable-length string. M represents the maximum column length. The range of M is 0 to 255 characters (1 to 255 prior to MySQL 4.0.2). In MySQL 5.0.3 this is extended to 65535 bytes. (The exact number of characters is depending on the character set). Note: Before 5.0.3, trailing spaces where removed when VARCHAR values was stored, which differs from the standard SQL specification. From MySQL 4.1.0 - 5.0.2 on, a VARCHAR column with a length specification greater than 255 is converted to the smallest TEXT type that can hold values of the given length. For example, VARCHAR(500) is converted to TEXT, and VARCHAR(200000) is converted to MEDIUMTEXT. This is a compatibility feature. However, this conversion affects trailing-space removal. VARCHAR is shorthand for CHARACTER VARYING. As of MySQL 4.1.2, the BINARY attribute is shorthand for specifying the binary collation of the column character set. Before 4.1.2, BINARY attribute causes the column to be treated as a binary string. In either case, sorting and comparisons become case sensitive. Starting from MySQL 5.0.3, VARCHAR is stored with a 1 byte or 2 byte length prefix + data. The length prefix is 1 byte if the storage size for the VARCHAR column is less than 256.

BINARY(M)

The BINARY type is similar to the CHAR type, but stores binary strings rather than non-binary strings. This type was added in MySQL 4.1.2.

VARBINARY(M)

The VARBINARY type is similar to the VARCHAR type, but stores binary strings rather than non-binary strings. This type was added in MySQL 4.1.2.

TINYBLOB

TINYTEXT

A BLOB or TEXT column with a maximum length of 255 (2^8 - 1) characters.

BLOB

TEXT

A BLOB or TEXT column with a maximum length of 65,535 (2^16 -1) characters.

MEDIUMBLOB

MEDIUMTEXT

A BLOB or TEXT column with a maximum length of 16,777,215 (2^24 - 1) characters.

LONGBLOB

LONGTEXT

A BLOB or TEXT column with a maximum length of 4,294,967,295 or 4GB (2^32 - 1) characters. Up to MySQL 3.23, the client/server protocol and MyISAM tables had a limit of 16MB per communication packet / table row. From MySQL 4.0, the maximum allowed length of LONGBLOB or LONGTEXT columns depends on the configured maximum packet size in the client/server protocol and available memory.

ENUM('value1','value2',...)

An enumeration. A string object that can have only one value, chosen from the list of values 'value1', 'value2', ..., NULL or the special '' error value. An ENUM column can have a maximum of 65,535 distinct values. ENUM values are represented internally as integers.

SET('value1','value2',...)

A set. A string object that can have zero or more values, each of which must be chosen from the list of values 'value1', 'value2', ... A SET column can have a maximum of 64 members. SET values are represented internally as integers.

11.2 Numeric Types

MySQL supports all of the standard SQL numeric data types. These types include the exact numeric data types (INTEGER, SMALLINT, DECIMAL, and NUMERIC), as well as the approximate numeric data types (FLOAT, REAL, and DOUBLE PRECISION). The keyword INT is a synonym for INTEGER, and the keyword DEC is a synonym for DECIMAL.

As an extension to the SQL standard, MySQL also supports the integer types TINYINT, MEDIUMINT, and BIGINT as listed in the following table.

Type	Bytes	Minimum Value	Maximum Value
		(Signed/Unsigned)	(Signed/Unsigned)
TINYINT	1	-128	127
		0	255
SMALLINT	2	-32768	32767
		0	65535
MEDIUMINT	3	-8388608	8388607
		0	16777215
INT	4	-2147483648	2147483647
		0	4294967295
BIGINT	8	-9223372036854775808	9223372036854775807
		0	18446744073709551615

Another extension is supported by MySQL for optionally specifying the display width of an integer value in parentheses following the base keyword for the type (for example, INT(4)). This optional display width specification is used to left-pad the display of values having a width less than the width specified for the column.

The display width does not constrain the range of values that can be stored in the column, nor the number of digits that will be displayed for values having a width exceeding that specified for the column.

When used in conjunction with the optional extension attribute ZEROFILL, the default padding of spaces is replaced with zeros. For example, for a column declared as INT(5) ZEROFILL, a value of 4 is retrieved as 00004. Note that if you store larger values than the display width in an integer column, you may experience problems when MySQL generates temporary tables for some complicated joins, because in these cases MySQL trusts that the data did fit into the original column width.

All integer types can have an optional (non-standard) attribute UNSIGNED. Unsigned values can be used when you want to allow only non-negative numbers in a column and you need a bigger upper numeric range for the column.

As of MySQL 4.0.2, floating-point and fixed-point types also can be UNSIGNED. As with integer types, this attribute prevents negative values from being stored in the column. However, unlike the integer types, the upper range of column values remains the same.

If you specify ZEROFILL for a numeric column, MySQL automatically adds the UNSIGNED attribute to the column.

The DECIMAL and NUMERIC types are implemented as the same type by MySQL. They are used to store values for which it is important to preserve exact precision, for example with monetary data. When declaring a column of one of these types, the precision and scale can be (and usually is) specified; for example:

salary DECIMAL(5,2)

In this example, 5 is the precision and 2 is the scale. The precision represents the number of significant decimal digits that will be stored for values, and the scale represents the number of digits that will be stored following the decimal point.

MySQL stores DECIMAL and NUMERIC values as strings, rather than as binary floating-point numbers, in order to preserve the decimal precision of those values. One character is used for each digit of the value, the decimal point (if the scale is greater than 0), and the `-' sign (for negative numbers). If the scale is 0, DECIMAL and NUMERIC values contain no decimal point or fractional part.

Standard SQL requires that the salary column be able to store any value with five digits and two decimals. In this case, therefore, the range of values that can be stored in the salary column is from -999.99 to 999.99. MySQL varies from this in two ways:

• On the positive end of the range, the column actually can store numbers up to 9999.99. For positive numbers, MySQL uses the byte reserved for the sign to extend the upper end of the range.
• DECIMAL columns in MySQL before 3.23 are stored differently and cannot represent all the values required by standard SQL. This is because for a type of DECIMAL(M,D), the value of M includes the bytes for the sign and the decimal point. The range of the salary column before MySQL 3.23 would be -9.99 to 99.99.

In standard SQL, the syntax DECIMAL(M) is equivalent to DECIMAL(M,0). Similarly, the syntax DECIMAL is equivalent to DECIMAL(M,0), where the implementation is allowed to decide the value of M. As of MySQL 3.23.6, both of these variant forms of the DECIMAL and NUMERIC data types are supported. The default value of M is 10. Before 3.23.6, M and D both must be specified explicitly.

The maximum range of DECIMAL and NUMERIC values is the same as for DOUBLE, but the actual range for a given DECIMAL or NUMERIC column can be constrained by the precision or scale for a given column. When such a column is assigned a value with more digits following the decimal point than are allowed by the specified scale, the value is converted to that scale. (The precise behavior is operating system-specific, but generally the effect is truncation to the allowable number of digits.) When a DECIMAL or NUMERIC column is assigned a value that exceeds the range implied by the specified (or default) precision and scale, MySQL stores the value representing the corresponding end point of that range.

For floating-point column types, MySQL uses four bytes for single-precision values and eight bytes for double-precision values.

The FLOAT type is used to represent approximate numeric data types. The SQL standard allows an optional specification of the precision (but not the range of the exponent) in bits following the keyword FLOAT in parentheses. The MySQL implementation also supports this optional precision specification, but the precision value is used only to determine storage size. A precision from 0 to 23 results in four-byte single-precision FLOAT column. A precision from 24 to 53 results in eight-byte double-precision DOUBLE column.

When the keyword FLOAT is used for a column type without a precision specification, MySQL uses four bytes to store the values. MySQL also supports variant syntax with two numbers given in parentheses following the FLOAT keyword. The first number represents the display width and the second number specifies the number of digits to be stored and displayed following the decimal point (as with DECIMAL and NUMERIC). When MySQL is asked to store a number for such a column with more decimal digits following the decimal point than specified for the column, the value is rounded to eliminate the extra digits when the value is stored.

In standard SQL, the REAL and DOUBLE PRECISION types do not accept precision specifications. MySQL supports a variant syntax with two numbers given in parentheses following the type name. The first number represents the display width and the second number specifies the number of digits to be stored and displayed following the decimal point. As an extension to the SQL standard, MySQL recognizes DOUBLE as a synonym for the DOUBLE PRECISION type. In contrast with the standard's requirement that the precision for REAL be smaller than that used for DOUBLE PRECISION, MySQL implements both as eight-byte double-precision floating-point values (unless the server SQL mode includes the REAL_AS_FLOAT option).

For maximum portability, code requiring storage of approximate numeric data values should use FLOAT or DOUBLE PRECISION with no specification of precision or number of decimal points.

When asked to store a value in a numeric column that is outside the column type's allowable range, MySQL clips the value to the appropriate endpoint of the range and stores the resulting value instead.

For example, the range of an INT column is -2147483648 to 2147483647. If you try to insert -9999999999 into an INT column, MySQL clips the value to the lower endpoint of the range and stores -2147483648 instead. Similarly, if you try to insert 9999999999, MySQL clips the value to the upper endpoint of the range and stores 2147483647 instead.

If the INT column is UNSIGNED, the size of the column's range is the same but its endpoints shift up to 0 and 4294967295. If you try to store -9999999999 and 9999999999, the values stored in the column are 0 and 4294967296.

Conversions that occur due to clipping are reported as ``warnings'' for ALTER TABLE, LOAD DATA INFILE, UPDATE, and multiple-row INSERT statements.

11.3 Date and Time Types

The date and time types for representing temporal values are DATETIME, DATE, TIMESTAMP, TIME, and YEAR. Each temporal type has a range of legal values, as well as a ``zero'' value that is used when you specify an illegal value that MySQL cannot represent. The TIMESTAMP type has special automatic updating behavior, described later on.

Starting from MySQL 5.0.2, MySQL will give warnings/errors if you try to insert an illegal date. You can get MySQL to accept certain dates, such as '1999-11-31', by using the ALLOW_INVALID_DATES SQL mode. (Before 5.0.2, this mode was the default behavior for MySQL). This is useful when you want to store the ``possibly wrong'' value the user has specified (for example, in a web form) in the database for future processing. Under this mode, MySQL verifies only that the month is in the range from 0 to 12 and that the day is in the range from 0 to 31. These ranges are defined to include zero because MySQL allows you to store dates where the day or month and day are zero in a DATE or DATETIME column. This is extremely useful for applications that need to store a birthdate for which you don't know the exact date. In this case, you simply store the date as '1999-00-00' or '1999-01-00'. If you store dates such as these, you should not expect to get correct results for functions such as DATE_SUB() or DATE_ADD that require complete dates. (If you don't want to allow zero in dates, you can use the NO_ZERO_IN_DATE SQL mode).

MySQL also allows you to store '0000-00-00' as a ``dummy date'' (if you are not using the NO_ZERO_DATE SQL mode). This is in some cases is more convenient than using NULL values.

By setting the sql_mode system variable to the appropriate mode values, You can more exactly what kind of dates you want MySQL to support. See section 5.2.2 The Server SQL Mode.

Here are some general considerations to keep in mind when working with date and time types:

• MySQL retrieves values for a given date or time type in a standard output format, but it attempts to interpret a variety of formats for input values that you supply (for example, when you specify a value to be assigned to or compared to a date or time type). Only the formats described in the following sections are supported. It is expected that you will supply legal values, and unpredictable results may occur if you use values in other formats.
• Dates containing two-digit year values are ambiguous because the century is unknown. MySQL interprets two-digit year values using the following rules:
  • Year values in the range 00-69 are converted to 2000-2069.
  • Year values in the range 70-99 are converted to 1970-1999.
• Although MySQL tries to interpret values in several formats, dates always must be given in year-month-day order (for example, '98-09-04'), rather than in the month-day-year or day-month-year orders commonly used elsewhere (for example, '09-04-98', '04-09-98').
• MySQL automatically converts a date or time type value to a number if the value is used in a numeric context and vice versa.
• When MySQL encounters a value for a date or time type that is out of range or otherwise illegal for the type (as described at the beginning of this section), it converts the value to the ``zero'' value for that type. The exception is that out-of-range TIME values are clipped to the appropriate endpoint of the TIME range. The following table shows the format of the ``zero'' value for each type. Note that the use of these values produces warnings if the NO_ZERO_DATE SQL mode is enabled.

  Column Type	``Zero'' Value
  DATETIME	'0000-00-00 00:00:00'
  DATE	'0000-00-00'
  TIMESTAMP	00000000000000
  TIME	'00:00:00'
  YEAR	0000

• The ``zero'' values are special, but you can store or refer to them explicitly using the values shown in the table. You can also do this using the values '0' or 0, which are easier to write.
• ``Zero'' date or time values used through MyODBC are converted automatically to NULL in MyODBC 2.50.12 and above, because ODBC can't handle such values.

11.3.1 The DATETIME, DATE, and TIMESTAMP Types

The DATETIME, DATE, and TIMESTAMP types are related. This section describes their characteristics, how they are similar, and how they differ.

The DATETIME type is used when you need values that contain both date and time information. MySQL retrieves and displays DATETIME values in 'YYYY-MM-DD HH:MM:SS' format. The supported range is '1000-01-01 00:00:00' to '9999-12-31 23:59:59'. (``Supported'' means that although earlier values might work, there is no guarantee that they will.)

The DATE type is used when you need only a date value, without a time part. MySQL retrieves and displays DATE values in 'YYYY-MM-DD' format. The supported range is '1000-01-01' to '9999-12-31'.

The TIMESTAMP column type has varying properties, depending on the MySQL version and the SQL mode the server is running in. These properties are described later in this section.

You can specify DATETIME, DATE, and TIMESTAMP values using any of a common set of formats:

• As a string in either 'YYYY-MM-DD HH:MM:SS' or 'YY-MM-DD HH:MM:SS' format. A ``relaxed'' syntax is allowed: Any punctuation character may be used as the delimiter between date parts or time parts. For example, '98-12-31 11:30:45', '98.12.31 11+30+45', '98/12/31 11*30*45', and '98@12@31 11^30^45' are equivalent.
• As a string in either 'YYYY-MM-DD' or 'YY-MM-DD' format. A ``relaxed'' syntax is allowed here, too. For example, '98-12-31', '98.12.31', '98/12/31', and '98@12@31' are equivalent.
• As a string with no delimiters in either 'YYYYMMDDHHMMSS' or 'YYMMDDHHMMSS' format, provided that the string makes sense as a date. For example, '19970523091528' and '970523091528' are interpreted as '1997-05-23 09:15:28', but '971122129015' is illegal (it has a nonsensical minute part) and becomes '0000-00-00 00:00:00'.
• As a string with no delimiters in either 'YYYYMMDD' or 'YYMMDD' format, provided that the string makes sense as a date. For example, '19970523' and '970523' are interpreted as '1997-05-23', but '971332' is illegal (it has nonsensical month and day parts) and becomes '0000-00-00'.
• As a number in either YYYYMMDDHHMMSS or YYMMDDHHMMSS format, provided that the number makes sense as a date. For example, 19830905132800 and 830905132800 are interpreted as '1983-09-05 13:28:00'.
• As a number in either YYYYMMDD or YYMMDD format, provided that the number makes sense as a date. For example, 19830905 and 830905 are interpreted as '1983-09-05'.
• As the result of a function that returns a value that is acceptable in a DATETIME, DATE, or TIMESTAMP context, such as NOW() or CURRENT_DATE.

Illegal DATETIME, DATE, or TIMESTAMP values are converted to the ``zero'' value of the appropriate type ('0000-00-00 00:00:00', '0000-00-00', or 00000000000000).

For values specified as strings that include date part delimiters, it is not necessary to specify two digits for month or day values that are less than 10. '1979-6-9' is the same as '1979-06-09'. Similarly, for values specified as strings that include time part delimiters, it is not necessary to specify two digits for hour, minute, or second values that are less than 10. '1979-10-30 1:2:3' is the same as '1979-10-30 01:02:03'.

Values specified as numbers should be 6, 8, 12, or 14 digits long. If a number is 8 or 14 digits long, it is assumed to be in YYYYMMDD or YYYYMMDDHHMMSS format and that the year is given by the first 4 digits. If the number is 6 or 12 digits long, it is assumed to be in YYMMDD or YYMMDDHHMMSS format and that the year is given by the first 2 digits. Numbers that are not one of these lengths are interpreted as though padded with leading zeros to the closest length.

Values specified as non-delimited strings are interpreted using their length as given. If the string is 8 or 14 characters long, the year is assumed to be given by the first 4 characters. Otherwise, the year is assumed to be given by the first 2 characters. The string is interpreted from left to right to find year, month, day, hour, minute, and second values, for as many parts as are present in the string. This means you should not use strings that have fewer than 6 characters. For example, if you specify '9903', thinking that will represent March, 1999, you will find that MySQL inserts a ``zero'' date into your table. This is because the year and month values are 99 and 03, but the day part is completely missing, so the value is not a legal date. However, as of MySQL 3.23, you can explicitly specify a value of zero to represent missing month or day parts. For example, you can use '990300' to insert the value '1999-03-00'.

You can to some extent assign values of one date type to an object of a different date type. However, there may be some alteration of the value or loss of information:

• If you assign a DATE value to a DATETIME or TIMESTAMP object, the time part of the resulting value is set to '00:00:00' because the DATE value contains no time information.
• If you assign a DATETIME or TIMESTAMP value to a DATE object, the time part of the resulting value is deleted because the DATE type stores no time information.
• Remember that although DATETIME, DATE, and TIMESTAMP values all can be specified using the same set of formats, the types do not all have the same range of values. For example, TIMESTAMP values cannot be earlier than 1970 or later than 2037. This means that a date such as '1968-01-01', while legal as a DATETIME or DATE value, is not a valid TIMESTAMP value and will be converted to 0 if assigned to such an object.

Be aware of certain pitfalls when specifying date values:

• The relaxed format allowed for values specified as strings can be deceiving. For example, a value such as '10:11:12' might look like a time value because of the `:' delimiter, but if used in a date context will be interpreted as the year '2010-11-12'. The value '10:45:15' will be converted to '0000-00-00' because '45' is not a legal month.
• The MySQL server performs only basic checking on the validity of a date: The ranges for year, month, and day are 1000 to 9999, 00 to 12, and 00 to 31, respectively. Any date containing parts not within these ranges is subject to conversion to '0000-00-00'. Please note that this still allows you to store invalid dates such as '2002-04-31'. To ensure that a date is valid, perform a check in your application.
• Dates containing two-digit year values are ambiguous because the century is unknown. MySQL interprets two-digit year values using the following rules:
  • Year values in the range 00-69 are converted to 2000-2069.
  • Year values in the range 70-99 are converted to 1970-1999.

11.3.1.1 TIMESTAMP Properties Prior to MySQL 4.1

The TIMESTAMP column type provides a type that you can use to automatically mark INSERT or UPDATE operations with the current date and time. If you have multiple TIMESTAMP columns in a table, only the first one is updated automatically. (From MySQL 4.1.2 on, you can specify which TIMESTAMP column updates; see section 11.3.1.2 TIMESTAMP Properties as of MySQL 4.1.)

Automatic updating of the first TIMESTAMP column in a table occurs under any of the following conditions:

• You explicitly set the column to NULL.
• The column is not specified explicitly in an INSERT or LOAD DATA INFILE statement.
• The column is not specified explicitly in an UPDATE statement and some other column changes value. An UPDATE that sets a column to the value it already has does not cause the TIMESTAMP column to be updated; if you set a column to its current value, MySQL ignores the update for efficiency.

TIMESTAMP columns other than the first can also be set to the current date and time. Just set the column to NULL or to any function that produces the current date and time (NOW(), CURRENT_TIMESTAMP).

You can set any TIMESTAMP column to a value different from the current date and time by setting it explicitly to the desired value. This is true even for the first TIMESTAMP column. You can use this property if, for example, you want a TIMESTAMP to be set to the current date and time when you create a row, but not to be changed whenever the row is updated later:

• Let MySQL set the column when the row is created. This initializes it to the current date and time.
• When you perform subsequent updates to other columns in the row, set the TIMESTAMP column explicitly to its current value:

  UPDATE tbl_name
      SET timestamp_col = timestamp_col,
          other_col1 = new_value1,
          other_col2 = new_value2, ...
  

Another way to maintain a column that records row-creation time is to use a DATETIME column that you initialize to NOW() when the row is created and leave alone for subsequent updates.

TIMESTAMP values may range from the beginning of 1970 to partway through the year 2037, with a resolution of one second. Values are displayed as numbers. When you store a value in a TIMESTAMP column, it is assumed to be represented in the current time zone, and is converted to UTC for storage. When you retrieve the value, it is converted from UTC back to the local time zone for display. Before MySQL 4.1.3, the server has a single time zone. As of 4.1.3, clients can set their time zone on a per-connection basis, as described in Time zone support.

The format in which MySQL retrieves and displays TIMESTAMP values depends on the display size, as illustrated by the following table. The ``full'' TIMESTAMP format is 14 digits, but TIMESTAMP columns may be created with shorter display sizes:

Column Type	Display Format
TIMESTAMP(14)	YYYYMMDDHHMMSS
TIMESTAMP(12)	YYMMDDHHMMSS
TIMESTAMP(10)	YYMMDDHHMM
TIMESTAMP(8)	YYYYMMDD
TIMESTAMP(6)	YYMMDD
TIMESTAMP(4)	YYMM
TIMESTAMP(2)	YY

All TIMESTAMP columns have the same storage size, regardless of display size. The most common display sizes are 6, 8, 12, and 14. You can specify an arbitrary display size at table creation time, but values of 0 or greater than 14 are coerced to 14. Odd-valued sizes in the range from 1 to 13 are coerced to the next higher even number.

TIMESTAMP columns store legal values using the full precision with which the value was specified, regardless of the display size. This has several implications:

• Always specify year, month, and day, even if your column types are TIMESTAMP(4) or TIMESTAMP(2). Otherwise, the value is not a legal date and 0 will be stored.
• If you use ALTER TABLE to widen a narrow TIMESTAMP column, information will be displayed that previously was ``hidden.''
• Similarly, narrowing a TIMESTAMP column does not cause information to be lost, except in the sense that less information is shown when the values are displayed.
• Although TIMESTAMP values are stored to full precision, the only function that operates directly on the underlying stored value is UNIX_TIMESTAMP(). Other functions operate on the formatted retrieved value. This means you cannot use a function such as HOUR() or SECOND() unless the relevant part of the TIMESTAMP value is included in the formatted value. For example, the HH part of a TIMESTAMP column is not displayed unless the display size is at least 10, so trying to use HOUR() on shorter TIMESTAMP values produces a meaningless result.

11.3.1.2 TIMESTAMP Properties as of MySQL 4.1

In MySQL 4.1 and up, the properties of the TIMESTAMP column type change in the ways described in this section.

From MySQL 4.1.0 on, TIMESTAMP display format differs from that of earlier MySQL releases:

• TIMESTAMP columns are displayed in the same format as DATETIME columns.
• Display widths (used as described in the preceding section) are no longer supported. In other words, for declarations such as TIMESTAMP(2), TIMESTAMP(4), and so on, the display width is ignored.

Beginning with MySQL 4.1.1, the MySQL server can be run in MAXDB mode. When the server runs in this mode, TIMESTAMP is identical with DATETIME. That is, if the server is running in MAXDB mode at the time that a table is created, TIMESTAMP columns are created as DATETIME columns. As a result, such columns use DATETIME display format, have the same range of values, and there is no automatic initialization or updating to the current date and time.

To enable MAXDB mode, set the server SQL mode to MAXDB at startup using the --sql-mode=MAXDB server option or by setting the global sql_mode variable at runtime:

mysql> SET GLOBAL sql_mode=MAXDB;

A client can cause the server to run in MAXDB mode for its own connection as follows:

mysql> SET SESSION sql_mode=MAXDB;

As of MySQL 5.0.2, MySQL will not accept timestamp values that includes a zero in the day or month column or values that are not a valid date. (The execption is the special value '0000-00-00 00:00:00'.)

Beginning with MySQL 4.1.2, you have more flexible control over when automatic TIMESTAMP initialization and updating occur and which column should have those behaviors:

• You can assign the current timestamp as the default value and the auto-update value, as before. But now it is possible to have just one automatic behavior or the other, or neither of them.
• You can specify which TIMESTAMP column to automatically initialize or update to the current date and time. This no longer need be the first TIMESTAMP column.

The following discussion describes the revised syntax and behavior. Note that this information applies only to TIMESTAMP columns for tables not created with MAXDB mode enabled. As noted earlier in this section, MAXDB mode causes columns to be created as DATETIME columns.

The following items summarize the pre-4.1.2 properties for TIMESTAMP initialization and updating:

The first TIMESTAMP column in table row automatically is set to the current timestamp when the record is created if the column is set to NULL or is not specified at all.

The first TIMESTAMP column in table row automatically is updated to the current timestamp when the value of any other column in the row is changed, unless the TIMESTAMP column explicitly is assigned a value other than NULL.

If a DEFAULT value is specified for the first TIMESTAMP column when the table is created, it is silently ignored.

Other TIMESTAMP columns in the table can be set to the current TIMESTAMP by assigning NULL to them, but they do not update automatically.

As of 4.1.2, you have more flexibility in deciding which TIMESTAMP column automatically is initialized and updated to the current timestamp. The rules are as follows:

If a DEFAULT value is specified for the first TIMESTAMP column in a table, it is not ignored. The default can be CURRENT_TIMESTAMP or a constant date and time value.

DEFAULT NULL is the same as DEFAULT CURRENT_TIMESTAMP for the first TIMESTAMP column. For any other TIMESTAMP column, DEFAULT NULL is treated as DEFAULT 0.

Any single TIMESTAMP column in a table can be set to be the one that is initialized to the current timestamp and/or updated automatically.

In a CREATE TABLE statement, the first TIMESTAMP column can be declared in any of the following ways:

• With both DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP clauses, the column has the current timestamp for its default value, and is automatically updated.
• With neither DEFAULT nor ON UPDATE clauses, it is the same as DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP.
• With a DEFAULT CURRENT_TIMESTAMP clause and no ON UPDATE clause, the column has the current timestamp for its default value but is not automatically updated.
• With no DEFAULT clause and with an ON UPDATE CURRENT_TIMESTAMP clause, the column has a default of 0 and is automatically updated.
• With a constant DEFAULT value and with ON UPDATE CURRENT_TIMESTAMP clause, the column has the given default and is automatically updated.

In other words, you can use the current timestamp for both the initial value and the auto-update value, or either one, or neither. (For example, you can specify ON UPDATE to get auto-update without also having the column auto-initialized.)

Any of CURRENT_TIMESTAMP, CURRENT_TIMESTAMP(), or NOW() can be used in the DEFAULT and ON UPDATE clauses. They all have the same effect.

The order of the two attributes does not matter. If both DEFAULT and ON UPDATE are specified for a TIMESTAMP column, either can precede the other.

Example. These statements are equivalent:

CREATE TABLE t (ts TIMESTAMP);
CREATE TABLE t (ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP
                             ON UPDATE CURRENT_TIMESTAMP);
CREATE TABLE t (ts TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
                             DEFAULT CURRENT_TIMESTAMP);

To specify automatic default or updating for a TIMESTAMP column other than the first one, you must suppress the automatic initialization and update behaviors for the first TIMESTAMP column by explicitly assigning it a constant DEFAULT value (for example, DEFAULT 0 or DEFAULT '2003-01-01 00:00:00'). Then for the other TIMESTAMP column, the rules are the same as for the first TIMESTAMP column, except that you cannot omit both of the DEFAULT and ON UPDATE clauses. If you do that, no automatic initialization or updating occurs.

Example. These statements are equivalent:

CREATE TABLE t (
    ts1 TIMESTAMP DEFAULT 0,
    ts2 TIMESTAMP DEFAULT CURRENT_TIMESTAMP
                  ON UPDATE CURRENT_TIMESTAMP);
CREATE TABLE t (
    ts1 TIMESTAMP DEFAULT 0,
    ts2 TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
                  DEFAULT CURRENT_TIMESTAMP);

Beginning with MySQL 4.1.3, you can set the current time zone on a per-connection basis, as described in Time zone support. TIMESTAMP values still are stored in UTC, but are converted from the current time zone for storage, and converted back to the current time zone for retrieval. As long as the time zone setting remains the same, you will get back the same value you store. If you store a TIMESTAMP value, then change the time zone and retrieve the value, it will be different than the value you stored. This occurs because the same time zone is not used for conversion in both directions. The current time zone is available as the value of the time_zone system variable.

Beginning with MySQL 4.1.6, you can include the NULL attribute in the definition of a TIMESTAMP column to allow the column to contain NULL values. Before MySQL 4.1.6 (and even as of 4.1.6 if the NULL attribute is not specified), setting the column to NULL sets it to the current timestamp.

11.3.2 The TIME Type

MySQL retrieves and displays TIME values in 'HH:MM:SS' format (or 'HHH:MM:SS' format for large hours values). TIME values may range from '-838:59:59' to '838:59:59'. The reason the hours part may be so large is that the TIME type may be used not only to represent a time of day (which must be less than 24 hours), but also elapsed time or a time interval between two events (which may be much greater than 24 hours, or even negative).

You can specify TIME values in a variety of formats:

• As a string in 'D HH:MM:SS.fraction' format. You can also use one of the following ``relaxed'' syntaxes: 'HH:MM:SS.fraction', 'HH:MM:SS', 'HH:MM', 'D HH:MM:SS', 'D HH:MM', 'D HH', or 'SS'. Here D represents days and can have a value from 0 to 34. Note that MySQL doesn't yet store the fraction part.
• As a string with no delimiters in 'HHMMSS' format, provided that it makes sense as a time. For example, '101112' is understood as '10:11:12', but '109712' is illegal (it has a nonsensical minute part) and becomes '00:00:00'.
• As a number in HHMMSS format, provided that it makes sense as a time. For example, 101112 is understood as '10:11:12'. The following alternative formats are also understood: SS, MMSS, HHMMSS, HHMMSS.fraction. Note that MySQL doesn't yet store the fraction part.
• As the result of a function that returns a value that is acceptable in a TIME context, such as CURRENT_TIME.

For TIME values specified as strings that include a time part delimiter, it is not necessary to specify two digits for hours, minutes, or seconds values that are less than 10. '8:3:2' is the same as '08:03:02'.

Be careful about assigning ``short'' TIME values to a TIME column. Without colons, MySQL interprets values using the assumption that the rightmost digits represent seconds. (MySQL interprets TIME values as elapsed time rather than as time of day.) For example, you might think of '1112' and 1112 as meaning '11:12:00' (12 minutes after 11 o'clock), but MySQL interprets them as '00:11:12' (11 minutes, 12 seconds). Similarly, '12' and 12 are interpreted as '00:00:12'. TIME values with colons, by contrast, are always treated as time of the day. That is '11:12' will mean '11:12:00', not '00:11:12'.

Values that lie outside the TIME range but are otherwise legal are clipped to the closest endpoint of the range. For example, '-850:00:00' and '850:00:00' are converted to '-838:59:59' and '838:59:59'.

Illegal TIME values are converted to '00:00:00'. Note that because '00:00:00' is itself a legal TIME value, there is no way to tell, from a value of '00:00:00' stored in a table, whether the original value was specified as '00:00:00' or whether it was illegal.

11.3.3 The YEAR Type

The YEAR type is a one-byte type used for representing years.

MySQL retrieves and displays YEAR values in YYYY format. The range is 1901 to 2155.

You can specify YEAR values in a variety of formats:

• As a four-digit string in the range '1901' to '2155'.
• As a four-digit number in the range 1901 to 2155.
• As a two-digit string in the range '00' to '99'. Values in the ranges '00' to '69' and '70' to '99' are converted to YEAR values in the ranges 2000 to 2069 and 1970 to 1999.
• As a two-digit number in the range 1 to 99. Values in the ranges 1 to 69 and 70 to 99 are converted to YEAR values in the ranges 2001 to 2069 and 1970 to 1999. Note that the range for two-digit numbers is slightly different from the range for two-digit strings, because you cannot specify zero directly as a number and have it be interpreted as 2000. You must specify it as a string '0' or '00' or it will be interpreted as 0000.
• As the result of a function that returns a value that is acceptable in a YEAR context, such as NOW().

Illegal YEAR values are converted to 0000.

11.3.4 Y2K Issues and Date Types

MySQL itself is year 2000 (Y2K) safe (see section 1.2.5 Year 2000 Compliance), but input values presented to MySQL may not be. Any input containing two-digit year values is ambiguous, because the century is unknown. Such values must be interpreted into four-digit form because MySQL stores years internally using four digits.

For DATETIME, DATE, TIMESTAMP, and YEAR types, MySQL interprets dates with ambiguous year values using the following rules:

• Year values in the range 00-69 are converted to 2000-2069.
• Year values in the range 70-99 are converted to 1970-1999.

Remember that these rules provide only reasonable guesses as to what your data values mean. If the heuristics used by MySQL do not produce the correct values, you should provide unambiguous input containing four-digit year values.

ORDER BY properly sorts TIMESTAMP or YEAR values that have two-digit years.

Some functions like MIN() and MAX() will convert a TIMESTAMP or YEAR to a number. This means that a value with a two-digit year will not work properly with these functions. The fix in this case is to convert the TIMESTAMP or YEAR to four-digit year format or use something like MIN(DATE_ADD(timestamp,INTERVAL 0 DAYS)).

11.4 String Types

The string types are CHAR, VARCHAR, BINARY, VARBINARY, BLOB, TEXT, ENUM, and SET. This section describes how these types work and how to use them in your queries.

11.4.1 The CHAR and VARCHAR Types

The CHAR and VARCHAR types are similar, but differ in the way they are stored and retrieved.

The length of a CHAR column is fixed to the length that you declare when you create the table. The length can be any value from 0 to 255. (Before MySQL 3.23, the length of CHAR may be from 1 to 255.) When CHAR values are stored, they are right-padded with spaces to the specified length. When CHAR values are retrieved, trailing spaces are removed.

Values in VARCHAR columns are variable-length strings. You can declare a VARCHAR column to be any length from 0 to 255, just as for CHAR columns. (Before MySQL 4.0.2, the length of VARCHAR may be from 1 to 255.) However, in contrast to CHAR, VARCHAR values are stored using only as many characters as are needed, plus one byte to record the length. Values are not padded; instead, trailing spaces are removed when values are stored. This space removal differs from the standard SQL specification.

No lettercase conversion takes place during storage or retrieval.

If you assign a value to a CHAR or VARCHAR column that exceeds the column's maximum length, the value is truncated to fit.

If you need a column for which trailing spaces are not removed, consider using a BLOB or TEXT type. If you want to store binary values such as results from an encryption or compression function that might contain arbitrary byte values, use a BLOB column rather than a CHAR or VARCHAR column, to avoid potential problems with trailing space removal that would change data values.

The following table illustrates the differences between the two types of columns by showing the result of storing various string values into CHAR(4) and VARCHAR(4) columns:

Value	CHAR(4)	Storage Required	VARCHAR(4)	Storage Required
''	' '	4 bytes	''	1 byte
'ab'	'ab '	4 bytes	'ab'	3 bytes
'abcd'	'abcd'	4 bytes	'abcd'	5 bytes
'abcdefgh'	'abcd'	4 bytes	'abcd'	5 bytes

The values retrieved from the CHAR(4) and VARCHAR(4) columns are the same in each case, because trailing spaces are removed from CHAR columns upon retrieval.

As of MySQL 4.1, values in CHAR and VARCHAR columns are sorted and compared according to the collation of the character set assigned to the column. Before MySQL 4.1, sorting and comparison are based on the collation of the server character set; you can declare the column with the BINARY attribute to cause sorting and comparison to be case sensitive using the underlying character code values rather then a lexical ordering. BINARY doesn't affect how the column is stored or retrieved.

From MySQL 4.1.0 on, column type CHAR BYTE is an alias for CHAR BINARY. This is a compatibility feature.

The BINARY attribute is sticky. This means that if a column marked BINARY is used in an expression, the whole expression is treated as a BINARY value.

From MySQL 4.1.0 on, the ASCII attribute can be specified for CHAR. It assigns the latin1 character set.

From MySQL 4.1.1 on, the UNICODE attribute can be specified for CHAR. It assigns the ucs2 character set.

MySQL may silently change the type of a CHAR or VARCHAR column at table creation time. See section 13.2.6.1 Silent Column Specification Changes.

11.4.2 The BINARY and VARBINARY Types

The BINARY and VARBINARY types are like CHAR and VARCHAR, except that they contain binary strings rather than non-binary strings. That is, they contain byte strings rather than character strings. This means they have no character set and compare in case sensitive fashion.

Before MySQL 4.1.2, BINARY(M) and VARBINARY(M) are treated as CHAR(M) BINARY and VARCHAR(M) BINARY. As of MySQL 4.1.2, BINARY and VARBINARY are available as distinct data types, and for CHAR(M) BINARY and VARCHAR(M) BINARY, the BINARY attribute does not cause the column to be treated as a binary string column. Instead, it causes the binary collation for the column character set to be used, but the column itself contains non-binary character strings rather than binary byte strings. For example, in 4.1 and up, CHAR(5) BINARY is treated as CHAR(5) CHARACTER SET latin1 COLLATE latin1_bin, assuming that the default character set is latin1.

11.4.3 The BLOB and TEXT Types

A BLOB is a binary large object that can hold a variable amount of data. The four BLOB types, TINYBLOB, BLOB, MEDIUMBLOB, and LONGBLOB, differ only in the maximum length of the values they can hold. See section 11.5 Column Type Storage Requirements.

The four TEXT types, TINYTEXT, TEXT, MEDIUMTEXT, and LONGTEXT, correspond to the four BLOB types and have the same maximum lengths and storage requirements.

BLOB columns are treated as binary strings, whereas TEXT columns are treated according to their character set. For BLOB columns, sorting and comparison is case sensitive. For TEXT columns, values are sorted and compared based on the collation of the character set assigned to the column as of MySQL 4.1. Before 4.1, TEXT sorting and comparison are based on the collation of the server character set.

No lettercase conversion takes place during storage or retrieval.

If you assign a value to a BLOB or TEXT column that exceeds the column type's maximum length, the value is truncated to fit.

In most respects, you can regard a TEXT column as a VARCHAR column that can be as big as you like. Similarly, you can regard a BLOB column as a VARCHAR BINARY column. The ways in which BLOB and TEXT differ from CHAR and VARCHAR are:

• There is no trailing-space removal for BLOB and TEXT columns when values are stored or retrieved. This differs from CHAR columns (trailing spaces are removed when values are retrieved) and from VARCHAR columns (trailing spaces are removed when values are stored).
• You can have indexes on BLOB and TEXT columns only as of MySQL 3.23.2 for MyISAM tables or MySQL 4.0.14 for InnoDB tables. Older versions of MySQL did not support indexing these column types.
• For indexes on BLOB and TEXT columns, you must specify an index prefix length. For CHAR and VARCHAR, a prefix length is optional.
• BLOB and TEXT columns cannot have DEFAULT values.

From MySQL 4.1.0 on, LONG and LONG VARCHAR map to the MEDIUMTEXT data type. This is a compatibility feature.

MySQL Connector/ODBC defines BLOB values as LONGVARBINARY and TEXT values as LONGVARCHAR.

Because BLOB and TEXT values may be extremely long, you may encounter some constraints in using them:

• Only the first max_sort_length bytes of the column are used when sorting. The default value of max_sort_length is 1024; this value can be changed using the --max_sort_length option when starting the mysqld server. See section 5.2.3 Server System Variables. As of MySQL 4.0.3, you can make more bytes signficant in sorting or grouping by increasing the value of max_sort_length at runtime. Any client can change the value of its session max_sort_length variable:

  mysql> SET max_sort_length = 2000;
  mysql> SELECT id, comment FROM tbl_name
      -> ORDER BY comment;
  

  Another way to use GROUP BY or ORDER BY on a BLOB or TEXT column containing long values when you want more than max_sort_length bytes to be significant is to convert the column value into a fixed-length object. The standard way to do this is with the SUBSTRING function. For example, the following statement causes 2000 bytes of the comment column to be taken into account for sorting:

  mysql> SELECT id, SUBSTRING(comment,1,2000) FROM tbl_name
      -> ORDER BY SUBSTRING(comment,1,2000);
  

  Before MySQL 3.23.2, you can group on an expression involving BLOB or TEXT values by using a column alias or by specifying the column position:

  mysql> SELECT id, SUBSTRING(comment,1,2000) AS b
      -> FROM tbl_name GROUP BY b;
  mysql> SELECT id, SUBSTRING(comment,1,2000)
      -> FROM tbl_name GROUP BY 2;
  

• The maximum size of a BLOB or TEXT object is determined by its type, but the largest value you actually can transmit between the client and server is determined by the amount of available memory and the size of the communications buffers. You can change the message buffer size by changing the value of the max_allowed_packet variable, but you must do so for both the server and your client program. For example, both mysql and mysqldump allow you to change the client-side max_allowed_packet value. See section 7.5.2 Tuning Server Parameters, section 8.3 mysql, the Command-Line Tool, and section 8.8 The mysqldump Database Backup Program.

Each BLOB or TEXT value is represented internally by a separately allocated object. This is in contrast to all other column types, for which storage is allocated once per column when the table is opened.

11.4.4 The ENUM Type

An ENUM is a string object with a value chosen from a list of allowed values that are enumerated explicitly in the column specification at table creation time.

The value may also be the empty string ('') or NULL under certain circumstances:

• If you insert an invalid value into an ENUM (that is, a string not present in the list of allowed values), the empty string is inserted instead as a special error value. This string can be distinguished from a ``normal'' empty string by the fact that this string has the numerical value 0. More about this later.
• If an ENUM column is declared to allow NULL, the NULL value is a legal value for the column, and the default value is NULL. If an ENUM column is declared NOT NULL, its default value is the first element of the list of allowed values.

Each enumeration value has an index:

• Values from the list of allowable elements in the column specification are numbered beginning with 1.
• The index value of the empty string error value is 0. This means that you can use the following SELECT statement to find rows into which invalid ENUM values were assigned:

  mysql> SELECT * FROM tbl_name WHERE enum_col=0;
  

• The index of the NULL value is NULL.

For example, a column specified as ENUM('one', 'two', 'three') can have any of the values shown here. The index of each value is also shown:

Value	Index
NULL	NULL
''	0
'one'	1
'two'	2
'three'	3

An enumeration can have a maximum of 65,535 elements.

Starting from MySQL 3.23.51, trailing spaces are automatically deleted from ENUM member values when the table is created.

Lettercase is irrelevant when you assign values to an ENUM column. However, values retrieved from the column later are displayed using the lettercase that was used in the column definition.

If you retrieve an ENUM value in a numeric context, the column value's index is returned. For example, you can retrieve numeric values from an ENUM column like this:

mysql> SELECT enum_col+0 FROM tbl_name;

If you store a number into an ENUM column, the number is treated as an index, and the value stored is the enumeration member with that index. (However, this will not work with LOAD DATA, which treats all input as strings.) It's not advisable to define an ENUM column with enumeration values that look like numbers, because this can easily become confusing. For example, the following column has enumeration members with string values of '0', '1', and '2', but numeric index values of 1, 2, and 3:

numbers ENUM('0','1','2')

ENUM values are sorted according to the order in which the enumeration members were listed in the column specification. (In other words, ENUM values are sorted according to their index numbers.) For example, 'a' sorts before 'b' for ENUM('a', 'b'), but 'b' sorts before 'a' for ENUM('b', 'a'). The empty string sorts before non-empty strings, and NULL values sort before all other enumeration values. To prevent unexpected results, specify the ENUM list in alphabetical order. You can also use GROUP BY CAST(col AS VARCHAR) or GROUP BY CONCAT(col) to make sure that the column is sorted lexically rather than by index number.

If you want to determine all possible values for an ENUM column, use SHOW COLUMNS FROM tbl_name LIKE enum_col and parse the ENUM definition in the second column of the output.

11.4.5 The SET Type

A SET is a string object that can have zero or more values, each of which must be chosen from a list of allowed values specified when the table is created. SET column values that consist of multiple set members are specified with members separated by commas (`,'). A consequence of this is that SET member values cannot themselves contain commas.

For example, a column specified as SET('one', 'two') NOT NULL can have any of these values:

''
'one'
'two'
'one,two'

A SET can have a maximum of 64 different members.

Starting from MySQL 3.23.51, trailing spaces are automatically deleted from SET member values when the table is created.

MySQL stores SET values numerically, with the low-order bit of the stored value corresponding to the first set member. If you retrieve a SET value in a numeric context, the value retrieved has bits set corresponding to the set members that make up the column value. For example, you can retrieve numeric values from a SET column like this:

mysql> SELECT set_col+0 FROM tbl_name;

If a number is stored into a SET column, the bits that are set in the binary representation of the number determine the set members in the column value. For a column specified as SET('a','b','c','d'), the members have the following decimal and binary values:

SET Member	Decimal Value	Binary Value
'a'	1	0001
'b'	2	0010
'c'	4	0100
'd'	8	1000

If you assign a value of 9 to this column, that is 1001 in binary, so the first and fourth SET value members 'a' and 'd' are selected and the resulting value is 'a,d'.

For a value containing more than one SET element, it does not matter what order the elements are listed in when you insert the value. It also does not matter how many times a given element is listed in the value. When the value is retrieved later, each element in the value will appear once, with elements listed according to the order in which they were specified at table creation time. If a column is specified as SET('a','b','c','d'), then 'a,d', 'd,a', and 'd,a,a,d,d' all will appear as 'a,d' when retrieved.

If you set a SET column to an unsupported value, the value will be ignored.

SET values are sorted numerically. NULL values sort before non-NULL SET values.

Normally, you search for SET values using the FIND_IN_SET() function or the LIKE operator:

mysql> SELECT * FROM tbl_name WHERE FIND_IN_SET('value',set_col)>0;
mysql> SELECT * FROM tbl_name WHERE set_col LIKE '%value%';

The first statement finds rows where set_col contains the value set member. The second is similar, but not the same: It finds rows where set_col contains value anywhere, even as a substring of another set member.

The following statements also are legal:

mysql> SELECT * FROM tbl_name WHERE set_col & 1;
mysql> SELECT * FROM tbl_name WHERE set_col = 'val1,val2';

The first of these statements looks for values containing the first set member. The second looks for an exact match. Be careful with comparisons of the second type. Comparing set values to 'val1,val2' will return different results than comparing values to 'val2,val1'. You should specify the values in the same order they are listed in the column definition.

If you want to determine all possible values for a SET column, use SHOW COLUMNS FROM tbl_name LIKE set_col and parse the SET definition in the second column of the output.

11.5 Column Type Storage Requirements

The storage requirements for each of the column types supported by MySQL are listed by category.

The maximum size of a row in a MyISAM table is 65,534 bytes. Each BLOB and TEXT column accounts for only five to nine bytes toward this size.

If a MyISAM or ISAM table includes any variable-length column types, the record format will also be variable length. When a table is created, MySQL may, under certain conditions, change a column from a variable-length type to a fixed-length type or vice versa. See section 13.2.6.1 Silent Column Specification Changes.

11.5.1 Storage Requirements for Numeric Types

Column Type	Storage Required
TINYINT	1 byte
SMALLINT	2 bytes
MEDIUMINT	3 bytes
INT, INTEGER	4 bytes
BIGINT	8 bytes
FLOAT(p)	4 bytes if 0 <= p <= 24, 8 bytes if 25 <= p <= 53
FLOAT	4 bytes
DOUBLE [PRECISION], item REAL	8 bytes
DECIMAL(M,D), NUMERIC(M,D)	M+2 bytes if D > 0, M+1 bytes if D = 0 (D+2, if M < D)

11.5.2 Storage Requirements for Date and Time Types

Column Type	Storage Required
DATE	3 bytes
DATETIME	8 bytes
TIMESTAMP	4 bytes
TIME	3 bytes
YEAR	1 byte

11.5.3 Storage Requirements for String Types

Column Type	Storage Required
CHAR(M)	M bytes, 0 <= M <= 255
VARCHAR(M)	L+1 bytes, where L <= M and 0 <= M <= 255
TINYBLOB, TINYTEXT	L+1 bytes, where L < 2^8
BLOB, TEXT	L+2 bytes, where L < 2^16
MEDIUMBLOB, MEDIUMTEXT	L+3 bytes, where L < 2^24
LONGBLOB, LONGTEXT	L+4 bytes, where L < 2^32
ENUM('value1','value2',...)	1 or 2 bytes, depending on the number of enumeration values (65,535 values maximum)
SET('value1','value2',...)	1, 2, 3, 4, or 8 bytes, depending on the number of set members (64 members maximum)

VARCHAR and the BLOB and TEXT types are variable-length types. For each, the storage requirements depend on the actual length of column values (represented by L in the preceding table), rather than on the type's maximum possible size. For example, a VARCHAR(10) column can hold a string with a maximum length of 10 characters. The actual storage required is the length of the string (L), plus 1 byte to record the length of the string. For the string 'abcd', L is 4 and the storage requirement is 5 bytes.

The BLOB and TEXT types require 1, 2, 3, or 4 bytes to record the length of the column value, depending on the maximum possible length of the type. See section 11.4.3 The BLOB and TEXT Types.

The size of an ENUM object is determined by the number of different enumeration values. One byte is used for enumerations with up to 255 possible values. Two bytes are used for enumerations with up to 65,535 values. See section 11.4.4 The ENUM Type.

The size of a SET object is determined by the number of different set members. If the set size is N, the object occupies (N+7)/8 bytes, rounded up to 1, 2, 3, 4, or 8 bytes. A SET can have a maximum of 64 members. See section 11.4.5 The SET Type.

11.6 Choosing the Right Type for a Column

For the most efficient use of storage, try to use the most precise type in all cases. For example, if an integer column will be used for values in the range from 1 to 99999, MEDIUMINT UNSIGNED is the best type. Of the types that represent all the required values, it uses the least amount of storage.

Accurate representation of monetary values is a common problem. In MySQL, you should use the DECIMAL type. This is stored as a string, so no loss of accuracy should occur. (Calculations on DECIMAL values may still be done using double-precision operations, however.) If accuracy is not too important, the DOUBLE type may also be good enough.

For high precision, you can always convert to a fixed-point type stored in a BIGINT. This allows you to do all calculations with integers and convert results back to floating-point values only when necessary.

11.7 Using Column Types from Other Database Engines

To make it easier to use code written for SQL implementations from other vendors, MySQL maps column types as shown in the following table. These mappings make it easier to import table definitions from other database engines into MySQL:

Other Vendor Type	MySQL Type
BINARY(M)	CHAR(M) BINARY (before MySQL 4.1.2)
CHAR VARYING(M)	VARCHAR(M)
FLOAT4	FLOAT
FLOAT8	DOUBLE
INT1	TINYINT
INT2	SMALLINT
INT3	MEDIUMINT
INT4	INT
INT8	BIGINT
LONG VARBINARY	MEDIUMBLOB
LONG VARCHAR	MEDIUMTEXT
LONG	MEDIUMTEXT (MySQL 4.1.0 on)
MIDDLEINT	MEDIUMINT
VARBINARY(M)	VARCHAR(M) BINARY (before MySQL 4.1.2)

As of MySQL 4.1.2, BINARY and VARBINARY are distinct data types and are not converted to CHAR BINARY and VARCHAR BINARY.

Column type mapping occurs at table creation time, after which the original type specifications are discarded. If you create a table with types used by other vendors and then issue a DESCRIBE tbl_name statement, MySQL reports the table structure using the equivalent MySQL types.

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