sqlite触发器中的条件插入语句

时间:2011-01-05 20:30:16

标签: sqlite triggers insert if-statement

sqlite触发器是否支持条件if / case / when语句?

假设我有以下设置:

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;

但它会出现语法错误Sqlite error near 'IF': syntax error"

2 个答案:

答案 0 :(得分:36)

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条件的触发器来达到同样的效果,参见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;

然后使用适当的条件为INSERT和UPDATE Case添加另一个触发器......

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

答案 1 :(得分:0)

以下是带有subselect的触发器的示例:

表格

CREATE TABLE A(
    ID INTEGER PRIMARY KEY,
    NAME TEXT
)
CREATE TABLE LOG(
    ID INTEGER PRIMARY KEY,
    DT TEXT
)


使用子选择

创建触发器
CREATE TRIGGER new_lns_historic AFTER INSERT 
    ON A 
    WHEN NEW.ID NOT IN (SELECT ID FROM LOG)
BEGIN
    INSERT INTO LOG VALUES (NEW.ID, DATETIME('NOW'));
END