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 10.6.1 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()'.
 
 Note: The `REPLACE()' function, unlike all other functions, always
 ignores the collation of the string input and performs a case-sensitive
 comparison.
 
 If a string input or function result is a binary string, the string has
 no character set or collation. This can be check by using the
 `CHARSET()' and `COLLATION()' functions, both of which return `binary'
 to indicate that their argument is a binary string:
 
      mysql> SELECT CHARSET(BINARY 'a'), COLLATION(BINARY 'a');
      +---------------------+-----------------------+
      | CHARSET(BINARY 'a') | COLLATION(BINARY 'a') |
      +---------------------+-----------------------+
      | binary              | binary                |
      +---------------------+-----------------------+
 
 For operations that combine multiple string inputs and return a single
 string output, the `aggregation rules' of standard SQL apply for
 determining the collation of the result:
 
    * If an explicit `COLLATE X' occurs, use X.
 
    * If explicit `COLLATE X' and `COLLATE Y' occur, raise an error.
 
    * Otherwise, if all collations are X, use X.
 
    * Otherwise, the result has no collation.
 
 For example, with `CASE ... WHEN a THEN b WHEN b THEN c COLLATE X END',
 the resulting 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 to `CAST()', `CHAR()', `CONV()', `FORMAT()',
 `HEX()', and `SPACE()'.
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