The default delimiter in the mysql client is the semicolon.
When creating stored programs from the command-line, it is likely you will need to differentiate between the regular delimiter and a delimiter inside a BEGIN END block. To understand better, consider the following example:
CREATE FUNCTION FortyTwo() RETURNS TINYINT DETERMINISTIC BEGIN DECLARE x TINYINT; SET x = 42; RETURN x; END;
If you enter the above line by line, the mysql client will treat the first semicolon, at the end of the
DECLARE x TINYINT line, as the end of the statement. Since that's only a partial definition, it will throw a syntax error, as follows:
CREATE FUNCTION FortyTwo() RETURNS TINYINT DETERMINISTIC BEGIN DECLARE x TINYINT; ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '' at line 3
The solution is to specify a distinct delimiter for the duration of the process, using the DELIMITER command. The delimiter can be any set of characters you choose, but it needs to be a distinctive set of characters that won't cause further confusion.
// is a common choice, and used throughout the knowledgebase.
Here's how the function could be successfully entered from the mysql client with the new delimiter.
DELIMITER // CREATE FUNCTION FortyTwo() RETURNS TINYINT DETERMINISTIC BEGIN DECLARE x TINYINT; SET x = 42; RETURN x; END // DELIMITER ;
At the end, the delimiter is restored to the default semicolon. The
\G delimiters can always be used, even when a custom delimiter is specified.