为什么SQL事务无法回滚

Question

如果某些课程的总注册人数超过50，我将尝试回滚事务。出于某种原因，即使我的if语句等于true（课程总数为60），也仍然会删除课程。

有任何想法吗？

BEGIN TRANSACTION T1
DELETE FROM Course WHERE Term = 'C'
    IF (SELECT SUM(Enrollment) FROM Course WHERE Term = 'C') > 50
    BEGIN;
        THROW 50002, 'Total Enrollment Greater Than 50... Rolling Back Transaction...', 1;
    ROLLBACK TRANSACTION T1;
    END;
COMMIT TRANSACTION T1

Answer 1

为什么在检查条件之前执行删除查询？

如果从条件满足Term = 'C' Course表中删除记录，则SELECT查询IF (SELECT SUM(Enrollment) FROM Course WHERE Term = 'C') > 50永不满足且不回滚。