Question

我有这样的事情：

表：

ct_lectures [id, l_id,name,position]

ct_teachers_lectures [id, t_id, l_id]

ct_teachers [id, name, surname, position]

ct_teachers_languages [id, t_id, lang_id]

首先，我列出所有讲座，然后我尝试找到与这些讲座相关并讲特定语言的老师：

SELECT DISTINCT ct_teachers.* FROM ct_teachers_lectures, ct_teachers, ct_teachers_languages WHERE (

(ct_teachers_lectures.l_id = 27 AND ct_teachers.id = ct_teachers_lectures.t_id AND ct_teachers_languages.t_id = ct_teachers_lectures.t_id) OR 
(ct_teachers_lectures.l_id = 67 AND ct_teachers.id = ct_teachers_lectures.t_id AND ct_teachers_languages.t_id = ct_teachers_lectures.t_id) OR 
(ct_teachers_lectures.l_id = 133 AND ct_teachers.id = ct_teachers_lectures.t_id AND ct_teachers_languages.t_id = ct_teachers_lectures.t_id) OR 
(ct_teachers_lectures.l_id = 262 AND ct_teachers.id = ct_teachers_lectures.t_id AND ct_teachers_languages.t_id = ct_teachers_lectures.t_id)

ORDER BY ct_teachers.id DESC LIMIT 30

甚至可以有15个讲座（上面的例子是4个）我想要搜索，所以会有15次这样的行：

(ct_teachers_lectures.l_id = **ID** AND ct_teachers.id = ct_teachers_lectures.t_id AND ct_teachers_languages.t_id = ct_teachers_lectures.t_id) OR

有没有更好的方法从数据库中获取这些教师而不是进行大查询？或者那些查询那么大是正常的吗？

Answer 1

SELECT DISTINCT 
      ct_t.* 
   FROM 
      ct_teachers ct_t 
         INNER JOIN ct_teachers_lectures ct_tlect 
            ON ct_tlect.t_id = ct_t.id 
         INNER JOIN ct_teachers_languages 
            ON ct_tlang.t_id = ct_tlect.t_id 
   WHERE 
          ct_tlect.l_id = 27 
       OR ct_tlect.l_id = 67 
       OR ct_tlect.l_id = 133 
       OR ct_tlect.l_id = 262 
   ORDER BY 
      ct_t.id DESC 
   LIMIT 30;

Answer 2

如果没有专门查看JOIN，可以选择使用UNION ALL代替OR的多个查询。

具有3个表的OR的MySQL查询优化

2 个答案: