sqlite触发器中的条件插入语句

Question

在sqlite触发器中是否支持条件if/case/when语句？

我们说我有以下设置:

CREATE TABLE someTable (id INTEGER PRIMARY KEY, someValue INTEGER);
CREATE TRIGGER update_another_table AFTER  INSERT ON someTable 
BEGIN
    IF(new.someValue==0)
        DELETE FROM another_table WHERE (...some condition);
    ELSE
        IF NOT EXISTS(SELECT anotherValue  FROM another_table  WHERE anotherValue =new.someValue)
            INSERT INTO another_table  VALUES(new.someValue, ...);
        ELSE
            UPDATE another_table SET anotherValue = new.someValue;
END;

但它会引发语法错误 Sqlite error near 'IF': syntax error"

Answer 1

这是一个语法错误,因为SQLite触发器的语法图不允许任何IF子句或CASE WHEN结构.

但是你可以通过定义两个或三个使用WHEN条件的触发器来实现相同的效果,请参阅http://sqlite.org/lang_createtrigger.html

所以你会为你的DELETE案例创建触发器,如下所示:

CREATE TRIGGER delete_from_other_table AFTER INSERT ON someTable
WHEN new.someValue = 0
BEGIN
   DELETE FROM anotherTable WHERE (... some condition );
END;

而且为INSERT和UPDATE Case添加另一个具有适当条件的触发器...

CREATE TRIGGER update_another_table AFTER INSERT ON someTable
WHEN new.someValue <> 0
BEGIN
   ...
END;