Question

我的JOIN遇到了一些困难，IS NULL ..

基本上我想要做的就是找到所有与我指定的某些群组类别ID不同的成员。

SELECT m.* FROM elvanto_members AS m
    LEFT JOIN elvanto_groups AS g ON g.deleted = 0
    LEFT JOIN elvanto_groups_categories AS gc ON gc.group_id = g.id AND (gc.category_id = '1' OR gc.category_id = '2')
    WHERE gr.id IS NULL

有些成员完全不属于任何组别类别，这就是为什么我将其作为LEFT JOIN。

我有道理吗？你知道如何解决这个问题吗？

Answer 1

试试这个：

SELECT m.* FROM elvanto_members AS m
WHERE 
  not exists 
  (
    SELECT 1 FROM 
     elvanto_groups AS g 
      INNER JOIN elvanto_groups_categories AS gc ON 
        gc.group_id = g.id
    WHERE
     gc.category_id IN ('1','2') AND
     g.id = m.group_id AND
     g.deleted = 0
  )

Answer 2

SELECT m.*
FROM   elvanto_members AS m
LEFT   JOIN elvanto_groups AS g ON g.id = m.group_id AND g.deleted = 0
LEFT   JOIN elvanto_groups_categories AS gc ON gc.group_id = g.id
                                           AND gc.category_id IN ('1','2')
WHERE  gc.group_id IS NULL
GROUP  BY m.*

我填写了问题中遗漏的内容 category_id真的是字符串类型吗？我希望它是数字的。然后这个表达式应该是：

 AND gc.category_id IN (1,2)

MySQL：连接表中的IS NULL

2 个答案: