|| is the ANSI standard string concatenation operator, supported by most databases (notably not MS SQL Server). MySQL also supports it, but you have to SET sql_mode="PIPES_AS_CONCAT"; or SET sql_mode="ANSI"; first.
|| is the ANSI standard string concatenation operator, supported by most databases (notably not MS SQL Server). MySQL also supports it, but you have to SET sql_mode="PIPES_AS_CONCAT"; or SET sql_mode="ANSI"; first.