10.3.5. Character String Literal Character Set and Collation
Every character string literal has a character set and a
collation.
A character string literal may have an optional character set
introducer and COLLATE clause:
[_charset_name]'string' [COLLATE collation_name]
Examples:
SELECT 'string';
SELECT _latin1'string';
SELECT _latin1'string' COLLATE latin1_danish_ci;
For the simple statement SELECT
'string', the string has
the character set and collation defined by the
character_set_connection and
collation_connection system variables.
The _charset_name
expression is formally called an
introducer. It tells the parser, “the
string that is about to follow uses character set
X.” Because this has confused
people in the past, we emphasize that an introducer does not
cause any conversion; it is strictly a signal that does not
change the string's value. An introducer is also legal before
standard hex literal and numeric hex literal notation
(x'literal' and
0xnnnn), and
before ? (parameter substitution when using
prepared statements within a programming language interface).
Examples:
SELECT _latin1 x'AABBCC';
SELECT _latin1 0xAABBCC;
SELECT _latin1 ?;
MySQL determines a literal's character set and collation in the
following manner:
If both _X and COLLATE
Y were specified, then
character set X and collation
Y are used.
If _X is specified but
COLLATE is not specified, then character
set X and its default collation
are used.
Otherwise, the character set and collation given by the
character_set_connection and
collation_connection system variables are
used.
Examples:
-
A string with latin1 character set and
latin1_german1_ci collation:
SELECT _latin1'Müller' COLLATE latin1_german1_ci;
-
A string with latin1 character set and
its default collation (that is,
latin1_swedish_ci):
SELECT _latin1'Müller';
-
A string with the connection default character set and
collation:
SELECT 'Müller';
Character set introducers and the COLLATE
clause are implemented according to standard SQL specifications.
