A summary of the string data types follows. For additional information about properties and storage requirements of the string types, see Section 11.4, “String Types”, and Section 11.7, “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 13.1.17.6, “Silent Column Specification Changes”.
MySQL interprets length specifications in character column
definitions in character units. 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.
The rules for assigning the character set and collation when
either or both of the CHARACTER SET and
COLLATE attributes are missing are
described in Section 10.1.3.5, “Column Character Set and Collation”.
CHARSET is a synonym for
CHARACTER SET.
Specifying the CHARACTER SET binary
attribute for a character string data type causes the column
to be created as the corresponding binary string data type:
CHAR becomes
BINARY,
VARCHAR becomes
VARBINARY, and
TEXT becomes
BLOB. For the
ENUM and
SET data types, this does not
occur; they are created as declared. Suppose that you
specify a table using this definition:
CREATE TABLE t
(
c1 VARCHAR(10) CHARACTER SET binary,
c2 TEXT CHARACTER SET binary,
c3 ENUM('a','b','c') CHARACTER SET binary
);
The resulting table has this definition:
CREATE TABLE t
(
c1 VARBINARY(10),
c2 BLOB,
c3 ENUM('a','b','c') CHARACTER SET binary
);
The BINARY attribute is shorthand for
specifying the table default character set and the binary
(_bin) collation of that character set.
In this case, comparison and sorting are based on numeric
character code values.
The ASCII attribute is shorthand for
CHARACTER SET latin1.
The UNICODE attribute is shorthand for
CHARACTER SET ucs2.
Character column comparison and sorting are based on the
collation assigned to the column. For the
CHAR,
VARCHAR,
TEXT,
ENUM, and
SET data types, you can declare a
column with a binary (_bin) collation or the
BINARY attribute to cause comparison and
sorting to use the underlying character code values rather than
a lexical ordering.
For additional information about use of character sets in MySQL, see Section 10.1, “Character Set Support”.
[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 in
characters. The range of M is 0
to 255. If M is omitted, the
length is 1.
Trailing spaces are removed when
CHAR values are retrieved
unless the
PAD_CHAR_TO_FULL_LENGTH
SQL mode is enabled.
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 uses utf8
as this predefined character set.
Section 10.1.3.7, “The National Character Set”.
The CHAR BYTE data type is an
alias for the BINARY data
type. This is a compatibility feature.
MySQL permits 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).
[NATIONAL] VARCHAR(
M)
[CHARACTER SET charset_name]
[COLLATE
collation_name]
A variable-length string. M
represents the maximum column length in characters. The
range of M is 0 to 65,535. The
effective maximum length of a
VARCHAR is subject to the
maximum row size (65,535 bytes, which is shared among all
columns) and the character set used. For example,
utf8 characters can require up to three
bytes per character, so a
VARCHAR column that uses the
utf8 character set can be declared to be
a maximum of 21,844 characters. See
Section C.10.4, “Limits on Table Column Count and Row Size”.
MySQL stores VARCHAR values
as a 1-byte or 2-byte length prefix plus data. The length
prefix indicates the number of bytes in the value. A
VARCHAR column uses one
length byte if values require no more than 255 bytes, two
length bytes if values may require more than 255 bytes.
MySQL follows the standard SQL specification, and does
not remove trailing spaces from
VARCHAR values.
VARCHAR is shorthand for
CHARACTER VARYING.
NATIONAL VARCHAR is the
standard SQL way to define that a
VARCHAR column should use
some predefined character set. MySQL uses
utf8 as this predefined character set.
Section 10.1.3.7, “The National Character Set”.
NVARCHAR is shorthand for
NATIONAL VARCHAR.
The BINARY type is similar to
the CHAR type, but stores
binary byte strings rather than nonbinary character strings.
M represents the column length in
bytes.
The VARBINARY type is similar
to the VARCHAR type, but
stores binary byte strings rather than nonbinary character
strings. M represents the maximum
column length in bytes.
A BLOB column with a maximum
length of 255 (28 − 1)
bytes. Each TINYBLOB value is
stored using a 1-byte length prefix that indicates the
number of bytes in the value.
TINYTEXT
[CHARACTER SET
charset_name]
[COLLATE
collation_name]
A TEXT column with a maximum
length of 255 (28 − 1)
characters. The effective maximum length is less if the
value contains multibyte characters. Each
TINYTEXT value is stored
using a 1-byte length prefix that indicates the number of
bytes in the value.
A BLOB column with a maximum
length of 65,535 (216 − 1)
bytes. Each BLOB value is
stored using a 2-byte length prefix that indicates the
number of bytes in the value.
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. The effective maximum length is less if the
value contains multibyte characters. Each
TEXT value is stored using a
2-byte length prefix that indicates the number of bytes in
the value.
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.
A BLOB column with a maximum
length of 16,777,215 (224 −
1) bytes. Each MEDIUMBLOB
value is stored using a 3-byte length prefix that indicates
the number of bytes in the value.
MEDIUMTEXT
[CHARACTER SET
charset_name]
[COLLATE
collation_name]
A TEXT column with a maximum
length of 16,777,215 (224 −
1) characters. The effective maximum length is less if the
value contains multibyte characters. Each
MEDIUMTEXT value is stored
using a 3-byte length prefix that indicates the number of
bytes in the value.
A BLOB column with a maximum
length of 4,294,967,295 or 4GB
(232 − 1) bytes. The
effective maximum length of
LONGBLOB columns depends on
the configured maximum packet size in the client/server
protocol and available memory. Each
LONGBLOB value is stored
using a 4-byte length prefix that indicates the number of
bytes in the value.
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
effective maximum length is less if the value contains
multibyte characters. The effective maximum length of
LONGTEXT
columns also depends on the configured maximum packet size
in the client/server protocol and available memory. Each
LONGTEXT
value is stored using a 4-byte length prefix that indicates
the number of bytes in the value.
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.
ENUM values are represented
internally as integers.
An ENUM column can have a
maximum of 65,535 distinct elements. (The practical limit is
less than 3000.) A table can have no more than 255 unique
element list definitions among its
ENUM and
SET columns considered as a
group. For more information on these limits, see
Section C.10.5, “Limits Imposed by .frm File Structure”.
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'... SET
values are represented internally as integers.
A SET column can have a
maximum of 64 distinct members. A table can have no more
than 255 unique element list definitions among its
ENUM and
SET columns considered as a
group. For more information on this limit, see
Section C.10.5, “Limits Imposed by .frm File Structure”.