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mysqlでjoinした結果をdelete

mysqlでjoinした結果をdeleteする場合の構文を忘れがちなので備忘録としてメモ。

テーブル作成

--- ユーザーメインテーブル
CREATE TABLE `user_main`(
  `user_id` int,
  `name` text,
  PRIMARY KEY  (`user_id`)
);

--- ユーザーサブテーブル
CREATE TABLE `user_sub`(
  `user_id` int,
  `type` int,
  PRIMARY KEY  (`user_id`)
);

データ登録

INSERT INTO user_main values(1, 'name1');
INSERT INTO user_main values(2, 'name2');
INSERT INTO user_main values(3, 'name3');

INSERT INTO user_sub values(1, 1);
INSERT INTO user_sub values(2, 2);
INSERT INTO user_sub values(3, 3);

JOINでSELECT

mysql> SELECT a.user_id, a.name, b.type FROM user_main a
LEFT JOIN user_sub b
ON a.user_id = b.user_id
WHERE b.type = 2;

+---------+-------+------+
| user_id | name  | type |
+---------+-------+------+
|       2 | name2 |    2 |
+---------+-------+------+
1 row in set (0.00 sec)

JOINでDELETE!

ポイントは"DELETE テーブル別名 FROM テーブル名 [AS] テーブル別名"とすること。

mysql> DELETE a FROM user_main a
LEFT JOIN user_sub b
ON a.user_id = b.user_id
WHERE b.type = 2;

Query OK, 1 row affected (0.00 sec)

mysql> SELECT * FROM user_main;
+---------+-------+
| user_id | name  |
+---------+-------+
|       1 | name1 |
|       3 | name3 |
+---------+-------+
2 rows in set (0.00 sec)

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Help us understand the problem. What are the problem?