String Function (string_function) 
A string_function is a function that supplies an alphanumeric value as a result.
Structure
Syntax
<string_function> ::= ALPHA(<string_spec>[,<unsigned_integer>]) | ASCII(<string_spec>) | CONCAT(<string_spec>,<string_spec>) | EXPAND(<string_spec>,<unsigned_integer>) | INITCAP(<string_spec>) | LFILL(<string_spec>,<string_literal>[,<unsigned_integer>]) | LOWER(<string_spec>) | LPAD(<string_spec>,<expression>,<string_literal>[,<unsigned_integer>]) | LTRIM(<string_spec>[,<string_spec>]) | MAPCHAR(<string_spec>[,<unsigned_integer>][,< mapchar_set_name>]) | REPLACE(<string_spec>,<string_spec>[,<string_spec>]) | RFILL(<string_spec>,<string_literal>[,<unsigned_integer>]) | RPAD(<string_spec>,<expression>,<string_literal>[,<unsigned_integer>]) | RTRIM(<string_spec>[,<string_spec>]) | SOUNDEX(<string_spec>) | SQLMODE() | SUBSTR(<string_spec>,<expression>[,<expression>]) | TRANSLATE(<string_spec>,<string_spec>,<string_spec>) | TRIM(<string_spec>[,<string_spec>]) | UPPER(<string_spec>) | <string_spec> || <string_spec> | <string_spec> & <string_spec> <string_spec> ::= <expression>
End of the code.
Explanation
<string_spec> || <string_spec> or <string_spec> & <string_spec> is used to represent a concatenation (CONCAT(x,X), x||y or x&y).
Only expressions that have an alphanumeric value are permitted as string specifications (string_spec).