MySQL: How do I use delimiters in triggers?

Question

Someone told me that I need to use a delimiter in my trigger. I\'m looking at the MySQL manual page, and I\'m finding it in the example; however, it\'s not in the generic d

Answer 1

Part 1

The delimiters are used for source objects like stored procedure/function, trigger or event. All these objects may have a body - code within BEGIN...END clause.

All statement in MySQL scripts should be ended with delimiter, the default is ';'. But what to do if source object has body with some statements, e,g:

INSERT INTO table1 VALUES(1);

CREATE PROCEDURE procedure1()
BEGIN
  SET @s = 'SELECT SQRT(POW(?,2) + POW(?,2)) AS hypotenuse';
  PREPARE stmt2 FROM @s;
  SET @a = 6;
  SET @b = 8;
  EXECUTE stmt2 USING @a, @b;
END;

INSERT INTO table1 VALUES(2);

How many statemants? 3 or 8? The answer is three, because script has two INSERTs and one CREATE PROCEDURE statements. As you see, CREATE PROCEDURE has some internal statements too; we should say to MySQL client that all these statement (inside BEGIN...END) - are part of ONE statement; we can do it with a help of delimiters:

INSERT INTO table1 VALUES(1);

DELIMITER $$

CREATE PROCEDURE procedure1()
BEGIN
  SET @s = 'SELECT SQRT(POW(?,2) + POW(?,2)) AS hypotenuse';
  PREPARE stmt2 FROM @s;
  SET @a = 6;
  SET @b = 8;
  EXECUTE stmt2 USING @a, @b;
END$$

DELIMITER ;

INSERT INTO table1 VALUES(2);

Note, when your trigger has no BEGIN...END clause, delimiters may be omitted.

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Part 2

Without delimiters the statement will be parsed as -

CREATE PROCEDURE procedure1()
BEGIN
  SET @s = 'SELECT SQRT(POW(?,2) + POW(?,2)) AS hypotenuse';

instead of -

CREATE PROCEDURE procedure1()
BEGIN
  SET @s = 'SELECT SQRT(POW(?,2) + POW(?,2)) AS hypotenuse';
  PREPARE stmt2 FROM @s;
  SET @a = 6;
  SET @b = 8;
  EXECUTE stmt2 USING @a, @b;
END