Question

鉴于

table1：

ID |名称

table2：

ID | table1_id | table3_id

表3：

ID |检查（类型= BOOLEAN）

现在我想在删除table1的相应行并删除相应的 table3 行时删除table2中的行。

我必须使用哪种SQL语句？

Answer 1

您需要两个触发器，一个用于检测已设置为1，一个用于检查从table1删除。这些有点“快速和肮脏”，但应该适用于任何最新的MySQL版本。

DELIMITER //

CREATE TRIGGER trig_table1 AFTER DELETE ON table1 
FOR EACH ROW
BEGIN
  DELETE table2.*  
  FROM table2
  JOIN table3 
    ON table3_id = table3.id
   AND table3.checked = 1
   AND table1_id = OLD.id;
END;
//

CREATE TRIGGER trig_table3 AFTER UPDATE ON table3
FOR EACH ROW
BEGIN
  DELETE table2.* 
  FROM table2
  LEFT JOIN table3 
    ON table3.id = OLD.id
   AND table3.checked = 0
  LEFT JOIN table1
    ON table1_id = table1.id
   AND table3_id = OLD.id
  WHERE table2.table3_id = OLD.id
    AND table3.id IS NULL
    AND table1.id IS NULL;
END;
//

An SQLfiddle to test with

Answer 2

你可以在MS SQL上尝试这样的东西。

delete table2 from table2 inner join table3 on table2.table3_id = table3.id
left join table1 on table1.id = table2.table1_id
where table3.checked = true and table1.id is null

SQL触发器语句

鉴于

2 个答案: