多对多查询过滤器

Question

我有以下问题。有两个表 - groups和students和第三数据透视表group_student。

查询来获取来自特定群体（ID：1,8）学生清楚......

SELECT DISTINCT s.* 
    FROM students AS s 
    Inner Join group_student AS gs ON gs.student_id = s.id 
    Inner Join groups AS g ON g.id = gs.group_id 
    WHERE g.id IN ("1","8") 

它的工作原理。但是，如何查询，如果我想只选择组ID为1的学生的片段。例如s.name = "john"。所以结果应该是：all students from group id 8 + all students with name "john" from group id 1。

感谢名单上岗:-)

Answer 1

试试这个：

SELECT DISTINCT s.* 
    FROM students AS s 
    Inner Join group_student AS gs ON gs.student_id = s.id 
    Inner Join groups AS g ON g.id = gs.group_id 
    WHERE g.id ="8" or (g.id="1" and s.name = "john") 

Answer 2

你可以使用UNION太

SELECT DISTINCT s.* 
    FROM students AS s 
    Inner Join group_student AS gs ON gs.student_id = s.id 
    Inner Join groups AS g ON g.id = gs.group_id 
    WHERE g.id = 8 
UNION 
SELECT DISTINCT s.* 
    FROM students AS s 
    Inner Join group_student AS gs ON gs.student_id = s.id 
    Inner Join groups AS g ON g.id = gs.group_id 
    WHERE gp.id="1" and s.name = "john" 

Answer 3

还有一个选项，避免DISTINCT和（可能是不需要的）加入到groups：

SELECT s.* 
FROM students AS s 
WHERE EXISTS 
     (SELECT * 
      FROM group_student AS gs 
      WHERE gs.student_id = s.id 
      AND ( gs.group_id = 8 
       OR (gs.group_id, s.name) = (1, 'john') 
       ) 
     )