SQL，如何将逻辑 ('not in' 转换为 'not exists' )

Question

Delete From StudentTb Where StudentType in (1, 2) and StudentI not in
(
    Select lg.StudentI From StudentLog lg
)

我尝试将上面的代码改成下面的...但是，我不确定它是否正确。

Delete From StudentTb Where StudentType in (1, 2) 
    and Not Exists 
    (
        Select 'x' 
        From StudentLog lg                          
        Where StudentI= lg.StudentI
    )

谁能帮帮我？

Answer 1

你做错的只是没有在子查询中指定正确的别名:

Delete From StudentTb Where StudentType in (1, 2) 
    and Not Exists 
    (
        Select 'x' 
        From StudentLog lg                          
        Where StudentTb.StudentI= lg.StudentI
    )

注意 - select 语句中的列不会影响最终结果，但仍然首选编写 * 而不是 'x'