Declare inside if condition showing syntax error - MYSQL Triggers - mysql

Question

I try to update some columns using trigger before insert
DROP TRIGGER IF EXISTS update_p_posts_places;
DELIMITER $$
CREATE TRIGGER update_p_posts_places BEFORE
INSERT
ON
`p_posts` FOR EACH ROW
BEGIN
DECLARE
p_post_group_id_ int;
SELECT
`p_post_subgroup`.`p_post_group_id`
INTO
p_post_group_id_
FROM
`p_post_subgroup`
WHERE
`p_post_subgroup`.`p_post_subgroup_id` = NEW.p_post_subgroup_id;
IF(p_post_group_id_ = 5) THEN
BEGIN
DECLARE
place1_id_ int;
place2_id_ int;
place3_id_ int;
place4_id_ int;
place5_id_ int;
SELECT
`Places`.`place1_id`,
`Places`.`place2_id`,
`Places`.`place3_id`,
`Places`.`place4_id`,
`Places`.`place5_id`
INTO
place1_id_, place2_id_, place3_id_, place4_id_, place5_id_
FROM
`Places`
WHERE
`Places`.`place5_id` = NEW.p_post_place_id LIMIT 1;
SET NEW.place5_id = place5_id_;
SET NEW.place1_id = place1_id_;
SET NEW.place2_id = place2_id_;
SET NEW.place3_id = place3_id_;
SET NEW.place4_id = place4_id_;
END $$
ELSE
SET NEW.place5_id = NULL;
END IF;
END $$
DELIMITER ;
It's showing some syntax errors.
#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DECLARE
place1_id_ int;
place2_id_ int;
' at line 20

Answer 1

Here is a working trigger. I tested creating it on MySQL 5.7.
CREATE TRIGGER update_p_posts_places BEFORE INSERT ON `p_posts`
FOR EACH ROW
BEGIN
-- all declarations must be before any other statements
DECLARE p_post_group_id_, place1_id_, place2_id_, place3_id_,
place4_id_, place5_id_ int;
SELECT
`p_post_subgroup`.`p_post_group_id`
INTO
p_post_group_id_
FROM
`p_post_subgroup`
WHERE
`p_post_subgroup`.`p_post_subgroup_id` = NEW.p_post_subgroup_id;
IF(p_post_group_id_ = 5) THEN
SELECT
`Places`.`place1_id`,
`Places`.`place2_id`,
`Places`.`place3_id`,
`Places`.`place4_id`,
`Places`.`place5_id`
INTO
place1_id_, place2_id_, place3_id_, place4_id_, place5_id_
FROM
`Places`
WHERE
`Places`.`place5_id` = NEW.p_post_place_id LIMIT 1;
SET NEW.place5_id = place5_id_;
SET NEW.place1_id = place1_id_;
SET NEW.place2_id = place2_id_;
SET NEW.place3_id = place3_id_;
SET NEW.place4_id = place4_id_;
ELSE
SET NEW.place5_id = NULL;
END IF;
END $$
You can use one DECLARE for multiple local variables, but you must do like var1, var2, var3, ... int. In other words, name the type only once at the end. See documentation: https://dev.mysql.com/doc/refman/8.0/en/declare-local-variable.html
No need for the BEGIN..END inside the IF and definitely do not use $$ until after the last END because that will terminate the parser's interpretation of your whole CREATE TRIGGER statement before it's complete.