Every “character” column (that is, a column of
type CHAR
,
VARCHAR
, or
TEXT
) has a column character
set and a column collation. Column definition syntax for
CREATE TABLE
and
ALTER TABLE
has optional
clauses for specifying the column character set and collation:
col_name
{CHAR | VARCHAR | TEXT} (col_length
) [CHARACTER SETcharset_name
] [COLLATEcollation_name
]
These clauses can also be used for
ENUM
and
SET
columns:
col_name
{ENUM | SET} (val_list
) [CHARACTER SETcharset_name
] [COLLATEcollation_name
]
Examples:
CREATE TABLE t1 ( col1 VARCHAR(5) CHARACTER SET latin1 COLLATE latin1_german1_ci ); ALTER TABLE t1 MODIFY col1 VARCHAR(5) CHARACTER SET latin1 COLLATE latin1_swedish_ci;
MySQL chooses the column character set and collation in the following manner:
If both CHARACTER SET
and
X
COLLATE
are specified, character set Y
X
and collation Y
are used.
CREATE TABLE t1 ( col1 CHAR(10) CHARACTER SET utf8 COLLATE utf8_unicode_ci ) CHARACTER SET latin1 COLLATE latin1_bin;
The character set and collation are specified for the
column, so they are used. The column has character set
utf8
and collation
utf8_unicode_ci
.
If CHARACTER SET
is specified
without X
COLLATE
, character set
X
and its default collation are
used.
CREATE TABLE t1 ( col1 CHAR(10) CHARACTER SET utf8 ) CHARACTER SET latin1 COLLATE latin1_bin;
The character set is specified for the column, but the
collation is not. The column has character set
utf8
and the default collation for
utf8
, which is
utf8_general_ci
. To see the default
collation for each character set, use the
SHOW COLLATION
statement.
If COLLATE
is specified without Y
CHARACTER SET
, the
character set associated with Y
and collation Y
are used.
CREATE TABLE t1 ( col1 CHAR(10) COLLATE utf8_polish_ci ) CHARACTER SET latin1 COLLATE latin1_bin;
The collation is specified for the column, but the
character set is not. The column has collation
utf8_polish_ci
and the character set is
the one associated with the collation, which is
utf8
.
Otherwise, the table character set and collation are used.
CREATE TABLE t1 ( col1 CHAR(10) ) CHARACTER SET latin1 COLLATE latin1_bin;
Neither the character set nor collation are specified for
the column, so the table defaults are used. The column has
character set latin1
and collation
latin1_bin
.
The CHARACTER SET
and
COLLATE
clauses are standard SQL.
If you use ALTER TABLE
to
convert a column from one character set to another, MySQL
attempts to map the data values, but if the character sets are
incompatible, there may be data loss.
User Comments
To change the character set (and collation) for all columns in an existing table, use...
ALTER TABLE tbl_name CONVERT TO CHARACTER SET charset_name [COLLATE collation_name];
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