mysql - 当我尝试通过连接从多个表中删除时出现 SQL 语法错误

Question

我必须从几个表中删除。这些表是费用、结果、休假和消息。它们都有一个名为 Student_id 的字段。我想从所有这些表中删除student_id值为3的行。但是我收到语法错误。

我做错了什么？这是我的查询

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

为什么不只删除四次呢？

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;

您可以在一个查询中执行此操作，如下所示:

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';

但这存在风险，其中一个表将没有学生的记录。如果 join 没有匹配项，则不会删除任何内容。