(mysql.info) charset-literal

 
 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'Mu"ller' COLLATE latin1_german1_ci;
 
    * A string with `latin1' character set and its default collation
      (that is, `latin1_swedish_ci'):
 
           SELECT _latin1'Mu"ller';
 
    * A string with the connection default character set and collation:
 
           SELECT 'Mu"ller';
 
 Character set introducers and the `COLLATE' clause are implemented
 according to standard SQL specifications.
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