The character set of the expression in the first SELECT statement determines the character set of the entire query. In the following example, the character set of <char_expression_1> is used as the character set for the entire query:
SELECT <char_expression_1> FROM <table_1> UNION SELECT <char_expression_2> FROM <table_2>;
If <char_expression_2> contains characters not included in the character set of <char_expression_1>, an error can result.
For example, if <char_expression_1> is CHARACTER SET LATIN, but <char_expression_2> is CHARACTER SET UNICODE, attempting to translate <char_expression_2> from UNICODE to LATIN results in an error if multi-byte characters are present in <char_expression_2>.