android - 如何使用删除触发器删除同一个表中的行？

Question

给出下表。

MY_TABLE

CREATE TABLE MY_TABLE (COL_1 VARCHAR, COL_2 VARCHAR);

我创建了以下触发器。

CREATE TRIGGER IF NOT EXIST MY_TRIGGER BEFORE DELETE ON MY_TABLE FOR EACH ROW BEGIN DELETE FROM MY_TABLE WHERE COL_2=currentrow.COL_1

每当要删除行时就会触发

MY_TRIGGER。我想要的是随后删除同一个表中条件成立的其他一些行。

我有两个问题:

1. 如何访问假设的当前行及其列的值？
2. 触发器会执行触发器运行删除查询吗？

Answer 1

您可以使用AFTER TRIGGER并使用old引用已删除的列:

CREATE TABLE MY_TABLE (COL_1 VARCHAR, COL_2 VARCHAR);
INSERT INTO My_Table VALUES (1,1), (1,2),(2,1),(2,2);

CREATE TRIGGER  MY_TRIGGER 
AFTER DELETE ON MY_TABLE 
FOR EACH ROW 
BEGIN 
  DELETE FROM MY_TABLE
  WHERE COL_2=old.COL_1;
END

DELETE FROM My_TABLE WHERE col_1 = 1;

SELECT * FROM My_Table;
-- 2 2

<强> DBFiddle Demo

更多关于CREATE TRIGGER

Both the WHEN clause and the trigger actions may access elements of the row being inserted, deleted or updated using references of the form "NEW.column-name" and "OLD.column-name", where column-name is the name of a column from the table that the trigger is associated with. OLD and NEW references may only be used in triggers on events for which they are relevant, as follows:

INSERT NEW references are valid

UPDATE NEW and OLD references are valid

DELETE OLD references are valid