在SQLite触发器中测试COUNT（）> X [英] Test for COUNT()>X inside SQLite trigger

问题描述

如何在SQLite的触发器中比较COUNT的结果？

How can I compare the result of a COUNT inside a trigger in SQLite?

到目前为止，这是我想出的代码：

So far, this is the code I've come up with:

CREATE TRIGGER mytrigger
BEFORE INSERT ON mytable
BEGIN
    SELECT CASE WHEN 
        SELECT COUNT (*) FROM mytable >= 3
    THEN
        RAISE(FAIL, "Activated - mytrigger.")
    END;
END;

无法编译为：

Error: near "SELECT": syntax error

如果我替换从mytable> = 3 中选择COUNT（*）与 1 == 1 ，它可以很好地编译，并触发总是执行。

If I replace SELECT COUNT (*) FROM mytable >= 3 with 1 == 1, it compiles fine, and the trigger executes always.

推荐答案

您需要在整个SELECT语句周围加上括号 SELECT COUNT（*）FROM mytable

You need to add parenthesis around the whole SELECT statement SELECT COUNT (*) FROM mytable

CREATE TRIGGER mytrigger
BEFORE INSERT ON mytable
BEGIN
    SELECT CASE WHEN 
        (SELECT COUNT (*) FROM mytable) >= 3
    THEN
        RAISE(FAIL, "Activated - mytrigger.")
    END;
END;

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