JavaScript Editor Source code editor     What Is Ajax 

Main Page

Chapter 11. Data Types

Table of Contents

11.1. Data Type Overview
11.1.1. Overview of Numeric Types
11.1.2. Overview of Date and Time Types
11.1.3. Overview of String Types
11.1.4. Data Type Default Values
11.2. Numeric Types
11.3. Date and Time Types
11.3.1. The DATETIME, DATE, and TIMESTAMP Types
11.3.2. The TIME Type
11.3.3. The YEAR Type
11.3.4. Year 2000 Issues and Date Types
11.4. String Types
11.4.1. The CHAR and VARCHAR Types
11.4.2. The BINARY and VARBINARY Types
11.4.3. The BLOB and TEXT Types
11.4.4. The ENUM Type
11.4.5. The SET Type
11.5. Data Type Storage Requirements
11.6. Choosing the Right Type for a Column
11.7. Using Data Types from Other Database Engines

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

MySQL also supports extensions for handing spatial data. Chapter 16, Spatial Extensions, provides information about these data types.

Several of the data type descriptions use these conventions:

11.1. Data Type Overview

11.1.1. Overview of Numeric Types

A summary of the numeric data types follows. For additional information, see Section 11.2, “Numeric Types”. Storage requirements are given in Section 11.5, “Data Type Storage Requirements”.

M indicates the maximum display width for integer types. The maximum legal display width is 255. Display width is unrelated to the range of values a type can contain, as described in Section 11.2, “Numeric Types”. For floating-point and fixed-point types, M is the total number of digits that can be stored.

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

Numeric data types that allow the UNSIGNED attribute also allow SIGNED. However, these data types are signed by default, so the SIGNED attribute has no effect.

SERIAL is an alias for BIGINT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE.

SERIAL DEFAULT VALUE in the definition of an integer column is an alias for NOT NULL AUTO_INCREMENT UNIQUE.

Warning: When you use subtraction between integer values where one is of type UNSIGNED, the result is unsigned unless the NO_UNSIGNED_SUBTRACTION SQL mode is enabled. See Section 12.9, “Cast Functions and Operators”.

  • BIT[(M)]

    A bit-field type. M indicates the number of bits per value, from 1 to 64. The default is 1 if M is omitted.

    This data type was added in MySQL 5.0.3 for MyISAM, and extended in 5.0.5 to MEMORY, InnoDB, and BDB. Before 5.0.3, BIT is a synonym for TINYINT(1).

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

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

  • BOOL, BOOLEAN

    These types are synonyms for TINYINT(1). A value of zero is considered false. Non-zero values are considered true:

    mysql> SELECT IF(0, 'true', 'false');
    +------------------------+
    | IF(0, 'true', 'false') |
    +------------------------+
    | false                  |
    +------------------------+
    
    mysql> SELECT IF(1, 'true', 'false');
    +------------------------+
    | IF(1, 'true', 'false') |
    +------------------------+
    | true                   |
    +------------------------+
    
    mysql> SELECT IF(2, 'true', 'false');
    +------------------------+
    | IF(2, 'true', 'false') |
    +------------------------+
    | true                   |
    +------------------------+

    However, the values TRUE and FALSE are merely aliases for 1 and 0, respectively, as shown here:

    mysql> SELECT IF(0 = FALSE, 'true', 'false');
    +--------------------------------+
    | IF(0 = FALSE, 'true', 'false') |
    +--------------------------------+
    | true                           |
    +--------------------------------+
    
    mysql> SELECT IF(1 = TRUE, 'true', 'false');
    +-------------------------------+
    | IF(1 = TRUE, 'true', 'false') |
    +-------------------------------+
    | true                          |
    +-------------------------------+
    
    mysql> SELECT IF(2 = TRUE, 'true', 'false');
    +-------------------------------+
    | IF(2 = TRUE, 'true', 'false') |
    +-------------------------------+
    | false                         |
    +-------------------------------+
    
    mysql> SELECT IF(2 = FALSE, 'true', 'false');
    +--------------------------------+
    | IF(2 = FALSE, 'true', 'false') |
    +--------------------------------+
    | false                          |
    +--------------------------------+

    The last two statements display the results shown because 2 is equal to neither 1 nor 0.

    We intend to implement full boolean type handling, in accordance with standard SQL, in a future MySQL release.

  • 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-sized 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 type 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.

    SERIAL is an alias for BIGINT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE.

    Some things you should be aware of with respect to BIGINT columns:

    • All arithmetic is done using signed BIGINT or DOUBLE values, so you should not 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 can handle BIGINT in the following cases:

      • When using integers to store large 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 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[(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. These are the theoretical limits, based on the IEEE standard. The actual range might be slightly smaller depending on your hardware or operating system.

    M is the total number of digits and D is the number of digits following the decimal point. If M and D are omitted, values are stored to the limits allowed by the hardware. A single-precision floating-point number is accurate to approximately 7 decimal places.

    UNSIGNED, if specified, disallows negative values.

    Using FLOAT might give you some unexpected problems because all calculations in MySQL are done with double precision. See Section B.1.5.7, “Solving Problems with No Matching Rows”.

  • 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. These are the theoretical limits, based on the IEEE standard. The actual range might be slightly smaller depending on your hardware or operating system.

    M is the total number of digits and D is the number of digits following the decimal point. If M and D are omitted, values are stored to the limits allowed by the hardware. A double-precision floating-point number is accurate to approximately 15 decimal places.

    UNSIGNED, if specified, disallows negative values.

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

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

  • FLOAT(p) [UNSIGNED] [ZEROFILL]

    A floating-point number. p represents the precision in bits, but MySQL uses this value only to determine whether to use FLOAT or DOUBLE for the resulting data type. If p is from 0 to 24, the data type becomes FLOAT with no M or D values. If p is from 25 to 53, the data type becomes DOUBLE with no M or D values. The range of the resulting column is the same as for the single-precision FLOAT or double-precision DOUBLE data types described earlier in this section.

    FLOAT(p) syntax is provided for ODBC compatibility.

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

    For MySQL 5.0.3 and above:

    A packed “exact” fixed-point number. M is the total number of digits (the precision) and D is the number of digits after the decimal point (the scale). The decimal point and (for negative numbers) the ‘-’ sign are not counted in M. If D is 0, values have no decimal point or fractional part. The maximum number of digits (M) for DECIMAL is 65 (64 from 5.0.3 to 5.0.5). The maximum number of supported decimals (D) is 30. If D is omitted, the default is 0. If M is omitted, the default is 10.

    UNSIGNED, if specified, disallows negative values.

    All basic calculations (+, -, *, /) with DECIMAL columns are done with a precision of 65 digits.

    Before MySQL 5.0.3:

    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 digits after the decimal point. 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 D is omitted, the default is 0. If M is omitted, the default is 10.

    UNSIGNED, if specified, disallows negative values.

    The behavior used by the server for DECIMAL columns in a table depends on the version of MySQL used to create the table. If your server is from MySQL 5.0.3 or higher, but you have DECIMAL columns in tables that were created before 5.0.3, the old behavior still applies to those columns. To convert the tables to the newer DECIMAL format, dump them with mysqldump and reload them.

  • DEC[(M[,D])] [UNSIGNED] [ZEROFILL], NUMERIC[(M[,D])] [UNSIGNED] [ZEROFILL], FIXED[(M[,D])] [UNSIGNED] [ZEROFILL]

    These types are synonyms for DECIMAL. The FIXED synonym is available for compatibility with other database systems.

11.1.2. Overview of Date and Time Types

A summary of the temporal data types follows. For additional information, see Section 11.3, “Date and Time Types”. Storage requirements are given in Section 11.5, “Data Type Storage Requirements”. Functions that operate on temporal values are described at Section 12.6, “Date and Time Functions”.

For the DATETIME and DATE range descriptions, “supported” means that although earlier values might work, there is no guarantee.

  • 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 assignment of 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 assignment of values to DATETIME columns using either strings or numbers.

  • TIMESTAMP

    A timestamp. The range is '1970-01-01 00:00:01' UTC to partway through the year 2038. TIMESTAMP values are stored as the number of seconds since the epoch ('1970-01-01 00:00:00' UTC). A TIMESTAMP cannot represent the value '1970-01-01 00:00:00' because that is equivalent to 0 seconds from the epoch and the value 0 is reserved for representing '0000-00-00 00:00:00', the “zeroTIMESTAMP value.

    A TIMESTAMP column is useful for recording the date and time of an INSERT or UPDATE operation. By default, the first TIMESTAMP column in a table is automatically set to the date and time of the most recent operation if you do not assign it a value yourself. You can also set any TIMESTAMP column to the current date and time by assigning it a NULL value. Variations on automatic initialization and update properties are described in Section 11.3.1.1, “TIMESTAMP Properties as of MySQL 4.1”.

    A TIMESTAMP value is returned as a string in the format 'YYYY-MM-DD HH:MM:SS' with a display width fixed at 19 characters. To obtain the value as a number, you should add +0 to the timestamp column.

    Note: The TIMESTAMP format that was used prior to MySQL 4.1 is not supported in MySQL 5.0; see MySQL 3.23, 4.0, 4.1 Reference Manual for information regarding the old format.

  • TIME

    A time. The range is '-838:59:59' to '838:59:59'. MySQL displays TIME values in 'HH:MM:SS' format, but allows assignment of 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 SUM() and AVG() aggregate functions do not work with temporal values. (They convert the values to numbers, which loses the part after the first non-numeric character.) To work around this problem, you can convert to numeric units, perform the aggregate operation, and convert back to a temporal value. Examples:

SELECT SEC_TO_TIME(SUM(TIME_TO_SEC(time_col))) FROM tbl_name;
SELECT FROM_DAYS(SUM(TO_DAYS(date_col))) FROM tbl_name;

11.1.3. Overview of String Types

A summary of the string data types follows. For additional information, see Section 11.4, “String Types”. Storage requirements are given in Section 11.5, “Data 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 13.1.5.1, “Silent Column Specification Changes”.

In MySQL 4.1 and up, string data types include some features that you may not have encountered in working with versions of MySQL prior to 4.1:

  • MySQL interprets length specifications in character column definitions in character units. (Before MySQL 4.1, column lengths were interpreted in bytes.) This applies to CHAR, VARCHAR, and the TEXT types.

  • Column definitions for many string data types can include attributes that specify the character set or collation of the column. These attributes apply to the CHAR, VARCHAR, the TEXT types, ENUM, and SET data types:

    • The CHARACTER SET attribute specifies the character set, and the COLLATE attribute specifies a collation for the character set. For example:

      CREATE TABLE t
      (
          c1 VARCHAR(20) CHARACTER SET utf8,
          c2 TEXT CHARACTER SET latin1 COLLATE latin1_general_cs
      );

      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 a case-sensitive collation.

      CHARSET is a synonym for CHARACTER SET.

    • The ASCII attribute is shorthand for CHARACTER SET latin1.

    • The UNICODE attribute is shorthand for CHARACTER SET ucs2.

    • The BINARY attribute is shorthand for specifying the binary collation of the column character set. In this case, sorting and comparison are based on numeric character values. (Before MySQL 4.1, BINARY caused a column to store binary strings and sorting and comparison were based on numeric byte values. This is the same as using character values for single-byte character sets, but not for multi-byte character sets.)

  • Character column sorting and comparison are based on the character set assigned to the column. (Before MySQL 4.1, sorting and comparison were based on the collation of the server character set.) For the CHAR, VARCHAR, TEXT, ENUM, and SET data types, you can declare a column with a binary collation or the BINARY attribute to cause sorting and comparison to use the underlying character code values rather than a lexical ordering.

Chapter 10, Character Set Support, provides additional information about use of character sets in MySQL.

  • [NATIONAL] CHAR(M) [CHARACTER SET charset_name] [COLLATE collation_name]

    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.

    Note: Trailing spaces are removed when CHAR values are retrieved.

    Before MySQL 5.0.3, 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.

    In MySQL 5.0.3 and later, if you attempt to set the length of a CHAR greater than 255, the CREATE TABLE or ALTER TABLE statement in which this is done fails with an error:

    mysql> CREATE TABLE c1 (col1 INT, col2 CHAR(500));
    ERROR 1074 (42000): Column length too big for column 'col' (max = 255);
    use BLOB or TEXT instead
    mysql> SHOW CREATE TABLE c1;
    ERROR 1146 (42S02): Table 'test.c1' doesn't exist

    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 some predefined character set. MySQL 4.1 and up uses utf8 as this predefined character set. Section 10.3.6, “National Character Set”.

    The CHAR BYTE data type is an alias for the BINARY data type. This is a compatibility feature.

    MySQL allows you to create a column of type CHAR(0). This is useful primarily when you have to be compliant with old applications that depend on the existence of a column but that do not actually use its value. CHAR(0) is also quite nice when you need a column that can take only two values: A column that is defined as CHAR(0) NULL occupies only one bit and can take only the values NULL and '' (the empty string).

  • CHAR [CHARACTER SET charset_name] [COLLATE collation_name]

    This type is a synonym for CHAR(1).

  • [NATIONAL] VARCHAR(M) [CHARACTER SET charset_name] [COLLATE collation_name]

    A variable-length string. M represents the maximum column length. In MySQL 5.0, the range of M is 0 to 255 before MySQL 5.0.3, and 0 to 65,535 in MySQL 5.0.3 and later. (The actual maximum length of a VARCHAR in MySQL 5.0 is determined by the maximum row size and the character set you use. The maximum effective column length starting with MySQL 5.0.3 is subject to a row size of 65,532 bytes.)

    Note: Before 5.0.3, trailing spaces were removed when VARCHAR values were stored, which differs from the standard SQL specification.

    Prior to MySQL 5.0.3, a VARCHAR column with a length specification greater than 255 was converted to the smallest TEXT type that could hold values of the given length. For example, VARCHAR(500) was converted to TEXT, and VARCHAR(200000) was converted to MEDIUMTEXT. This was a compatibility feature. However, this conversion affected trailing-space removal.

    VARCHAR is shorthand for CHARACTER VARYING.

    VARCHAR values are stored using as many characters as are needed, plus one byte to record the length (two bytes for columns that are declared with a length longer than 255).

  • BINARY(M)

    The BINARY type is similar to the CHAR type, but stores binary byte strings rather than non-binary character strings.

  • VARBINARY(M)

    The VARBINARY type is similar to the VARCHAR type, but stores binary byte strings rather than non-binary character strings.

  • TINYBLOB

    A BLOB column with a maximum length of 255 (28 – 1) bytes.

  • TINYTEXT [CHARACTER SET charset_name] [COLLATE collation_name]

    A TEXT column with a maximum length of 255 (28 – 1) characters.

  • BLOB[(M)]

    A BLOB column with a maximum length of 65,535 (216 – 1) bytes.

    An optional length M can be given for this type. If this is done, MySQL creates the column as the smallest BLOB type large enough to hold values M bytes long.

  • TEXT[(M)] [CHARACTER SET charset_name] [COLLATE collation_name]

    A TEXT column with a maximum length of 65,535 (216 – 1) characters.

    An optional length M can be given for this type. If this is done, MySQL creates the column as the smallest TEXT type large enough to hold values M characters long.

  • MEDIUMBLOB

    A BLOB column with a maximum length of 16,777,215 (224 – 1) bytes.

  • MEDIUMTEXT [CHARACTER SET charset_name] [COLLATE collation_name]

    A TEXT column with a maximum length of 16,777,215 (224 – 1) characters.

  • LONGBLOB

    A BLOB column with a maximum length of 4,294,967,295 or 4GB (232 – 1) bytes. The maximum effective (permitted) length of LONGBLOB columns depends on the configured maximum packet size in the client/server protocol and available memory.

  • LONGTEXT [CHARACTER SET charset_name] [COLLATE collation_name]

    A TEXT column with a maximum length of 4,294,967,295 or 4GB (232 – 1) characters. The maximum effective (permitted) length of LONGTEXT columns depends on the configured maximum packet size in the client/server protocol and available memory.

  • ENUM('value1','value2',...) [CHARACTER SET charset_name] [COLLATE collation_name]

    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',...) [CHARACTER SET charset_name] [COLLATE collation_name]

    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.

11.1.4. Data Type Default Values

The DEFAULT value clause in a data type specification indicates a default value for a column. With one exception, the default value must be a constant; it cannot be a function or an expression. This means, for example, that you cannot set the default for a date column to be the value of a function such as NOW() or CURRENT_DATE. The exception is that you can specify CURRENT_TIMESTAMP as the default for a TIMESTAMP column. See Section 11.3.1.1, “TIMESTAMP Properties as of MySQL 4.1”.

Prior to MySQL 5.0.2, if a column definition includes no explicit DEFAULT value, MySQL determines the default value as follows:

If the column can take NULL as a value, the column is defined with an explicit DEFAULT NULL clause.

If the column cannot take NULL as the value, MySQL defines the column with an explicit DEFAULT clause, using the implicit default value for the column data type. Implicit defaults are defined as follows:

  • For numeric types other than integer types declared with the AUTO_INCREMENT attribute, the default is 0. For an AUTO_INCREMENT column, the default value is the next value in the sequence.

  • For date and time types other than TIMESTAMP, the default is the appropriate “zero” value for the type. For the first TIMESTAMP column in a table, the default value is the current date and time. See Section 11.3, “Date and Time Types”.

  • For string types other than ENUM, the default value is the empty string. For ENUM, the default is the first enumeration value.

BLOB and TEXT columns cannot be assigned a default value.

As of MySQL 5.0.2, if a column definition includes no explicit DEFAULT value, MySQL determines the default value as follows:

If the column can take NULL as a value, the column is defined with an explicit DEFAULT NULL clause. This is the same as before 5.0.2.

If the column cannot take NULL as the value, MySQL defines the column with no explicit DEFAULT clause. For data entry, if an INSERT or REPLACE statement includes no value for the column, MySQL handles the column according to the SQL mode in effect at the time:

  • If strict SQL mode is not enabled, MySQL sets the column to the implicit default value for the column data type.

  • If strict mode is enabled, an error occurs for transactional tables and the statement is rolled back. For non-transactional tables, an error occurs, but if this happens for the second or subsequent row of a multiple-row statement, the preceding rows will have been inserted.

Suppose that a table t is defined as follows:

CREATE TABLE t (i INT NOT NULL);

In this case, i has no explicit default, so in strict mode each of the following statements produce an error and no row is inserted. When not using strict mode, only the third statement produces an error; the implicit default is inserted for the first two statements, but the third fails because DEFAULT(i) cannot produce a value:

INSERT INTO t VALUES();
INSERT INTO t VALUES(DEFAULT);
INSERT INTO t VALUES(DEFAULT(i));

See Section 5.2.6, “SQL Modes”.

For a given table, you can use the SHOW CREATE TABLE statement to see which columns have an explicit DEFAULT clause.

SERIAL DEFAULT VALUE in the definition of an integer column is an alias for NOT NULL AUTO_INCREMENT UNIQUE.

JavaScript Editor Source code editor     What Is Ajax