當我試圖通過加入從多個表中刪除SQL語法錯誤

Question

我必須從幾個表中刪除。這些表格是費用，結果，葉子和消息。他們都有一個名爲student_id的字段。我想從所有這些表中的student_id值爲3的行中刪除。但是我收到語法錯誤。

我在做什麼錯？這裏是我的查詢

delete from fees join results on fees.student_id = results.student_id join messages on results.student_id = messages.student_id join leaves on messages.student_id = leaves.student_id where fees.student_id = '3'; 

Answer 1

爲什麼不只是做四個刪除？

delete from fees where student_id = 3; 
delete from results where student_id = 3; 
delete from leaves where student_id = 3; 
delete from messages where student_id = 3; 

您可以在一個查詢中這樣做，因爲：

delete f, r, l, m 
    from fees f join 
     results r 
     on f.student_id = r.student_id join 
     messages m 
     on r.student_id = m.student_id join 
     leaves l 
     on m.student_id = l.student_id 
    where f.student_id = '3'; 

這因小失大，雖然，其中一個表將會對學生沒有任何記錄。如果join沒有匹配，則不會被刪除。