多對多查詢過濾器

Question

我有以下問題。有兩個表 - groups和students和第三數據透視表group_student。

查詢來獲取來自特定羣體（ID：1,8）學生清楚......

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，如何查詢，如果我想只選擇組ID爲1的學生的片段。例如s.name = "john"。所以結果應該是：all students from group id 8 + all students with name "john" from group id 1。

感謝名單上崗:-)

Answer 1

試試這個：

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

還有一個選項，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') 
       ) 
     )