(mysql.info.gz) Charset-result

(mysql.info.gz) Charset-operations

 
 10.4.1 Result Strings
 ---------------------
 
 MySQL has many operators and functions that return a string.  This
 section answers the question: What is the character set and collation
 of such a string?
 
 For simple functions that take string input and return a string result
 as output, the output's character set and collation are the same as
 those of the principal input value. For example, `UPPER(X)' returns a
 string whose character string and collation are the same as that of X.
 The same applies for `INSTR()', `LCASE()', `LOWER()', `LTRIM()',
 `MID()', `REPEAT()', `REPLACE()', `REVERSE()', `RIGHT()', `RPAD()',
 `RTRIM()', `SOUNDEX()', `SUBSTRING()', `TRIM()', `UCASE()', and
 `UPPER()'.  (Also note: The `REPLACE()' function, unlike all other
 functions, ignores the collation of the string input and performs a
 case-insensitive comparison every time.)
 
 For operations that combine multiple string inputs and return a single
 string output, the "aggregation rules" of standard SQL apply:
 
    * If an explicit `COLLATE X' occurs, then use `X'
 
    * If an explicit `COLLATE X' and `COLLATE Y' occur, then error
 
    * Otherwise, if all collations are `X', then use `X'
 
    * Otherwise, the result has no collation
 
 
 For example, with `CASE ... WHEN a THEN b WHEN b THEN c COLLATE X END',
 the resultant collation is `X'. The same applies for `CASE', `UNION',
 `||', `CONCAT()', `ELT()', `GREATEST()', `IF()', and `LEAST()'.
 
 For operations that convert to character data, the character set and
 collation of the strings that result from the operations are defined by
 the `character_set_connection' and `collation_connection' system
 variables.  This applies for `CAST()', `CHAR()', `CONV()', `FORMAT()',
 `HEX()', and `SPACE()'.

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