Table of contents
The type of data fields defined in MySQL is very important to the optimization of your database.
MySQL supports a variety of types, which can be roughly divided into three categories: numeric, date/time, and string (character) types.
value type
MySQL supports all standard SQL numeric data types.
These types include strictly numeric data types (INTEGER, SMALLINT, DECIMAL, and NUMERIC), and 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.
The BIT data type holds bit field values and supports MyISAM, MEMORY, InnoDB, and BDB tables.
As an extension to the SQL standard, MySQL also supports the integer types TINYINT, MEDIUMINT, and BIGINT. The table below shows the storage and range required for each integer type.
| type | size | range (signed) | range (unsigned) | use |
|---|---|---|---|---|
| TINYINT | 1 Bytes | (-128，127) | (0，255) | small integer value |
| SMALLINT | 2 Bytes | (-32 768，32 767) | (0，65 535) | big integer value |
| MEDIUMINT | 3 Bytes | (-8 388 608，8 388 607) | (0，16 777 215) | big integer value |
| INT or INTEGER | 4 Bytes | (-2 147 483 648，2 147 483 647) | (0，4 294 967 295) | big integer value |
| BIGINT | 8 Bytes | (-9,223,372,036,854,775,808，9 223 372 036 854 775 807) | (0，18 446 744 073 709 551 615) | extremely large integer value |
| FLOAT | 4 Bytes | (-3.402 823 466 E+38，-1.175 494 351 E-38)，0，(1.175 494 351 E-38，3.402 823 466 351 E+38) | 0，(1.175 494 351 E-38，3.402 823 466 E+38) | single-precision floating-point value |
| DOUBLE | 8 Bytes | (-1.797 693 134 862 315 7 E+308，-2.225 073 858 507 201 4 E-308)，0，(2.225 073 858 507 201 4 E-308，1.797 693 134 862 315 7 E+308 ) | 0，(2.225 073 858 507 201 4 E-308，1.797 693 134 862 315 7 E+308) | double-precision floating-point value |
| DECIMAL | For DECIMAL(M,D), if M>D, it is M+2, otherwise it is D+2 | depends on the value of M and D | depends on the value of M and D | decimal value |
date and time type
Date and time types representing time values are DATETIME, DATE, TIMESTAMP, TIME, and YEAR.
Each time type has a range of valid values and a "zero" value, which is used when specifying an invalid value that MySQL cannot represent.
The TIMESTAMP type has a proprietary automatic update feature, which will be described later.
| type | size (bytes) | scope | Format | use |
|---|---|---|---|---|
| DATE | 3 | 1000-01-01/9999-12-31 | YYYY-MM-DD | date value |
| TIME | 3 | '-838:59:59'/'838:59:59' | HH:MM:SS | time value or duration |
| YEAR | 1 | 1901/2155 | YYYY | year value |
| DATETIME | 8 | 1000-01-01 00:00:00/9999-12-31 23:59:59 | YYYY-MM-DD HH:MM:SS | Mixed date and time values |
| TIMESTAMP | 4 | 1970-01-01 00:00:00/2038 The end time is 2147483647 seconds, Beijing time 2038-1-19 11:14:07 , GMT 03:14:07 on January 19, 2038 | YYYYMMDD HHMMSS | Mixed date and time values, timestamps |
string type
String types refer to CHAR, VARCHAR, BINARY, VARBINARY, BLOB, TEXT, ENUM, and SET. This section describes how these types work and how to use them in queries.
| type | size | use |
|---|---|---|
| CHAR | 0-255 bytes | fixed length string |
| VARCHAR | 0-65535 bytes | variable length string |
| TINYBLOB | 0-255 bytes | Binary string of no more than 255 characters |
| TINYTEXT | 0-255 bytes | short text string |
| BLOB | 0-65 535 bytes | Long text data in binary form |
| TEXT | 0-65 535 bytes | long text data |
| MEDIUMBLOB | 0-16 777 215 bytes | Medium-length text data in binary form |
| MEDIUMTEXT | 0-16 777 215 bytes | medium length text data |
| LUNG BLOB | 0-4 294 967 295 bytes | Very large text data in binary form |
| LONGTEXT | 0-4 294 967 295 bytes | extremely large text data |
Note : n in the brackets of char(n) and varchar(n) represents the number of characters, not the number of bytes. For example, CHAR(30) can store 30 characters.
CHAR and VARCHAR types are similar, but they are stored and retrieved differently. They also differ in terms of maximum length and whether or not trailing spaces are preserved. No case conversion is done during storage or retrieval.
BINARY and VARBINARY are similar to CHAR and VARCHAR except that they contain binary strings rather than nonbinary strings. That is, they contain byte strings rather than character strings. This means they have no character set, and sorting and comparisons are based on the numeric value of the column value bytes.
A BLOB is a binary large object that can hold variable amounts of data. There are 4 BLOB types: TINYBLOB, BLOB, MEDIUMBLOB, and LONGBLOB. They differ in that they can accommodate different storage ranges.
There are 4 TEXT types: TINYTEXT, TEXT, MEDIUMTEXT, and LONGTEXT. The corresponding four BLOB types have different maximum storage lengths, which can be selected according to the actual situation.