Question

我正在尝试通过联接转换下面的查询，

SELECT DISTINCT req.*
FROM request req
WHERE (req.user_id IN (
            SELECT id from user where id in (SELECT user_id FROM team_member team WHERE team.team_id IN ('344', '723')) and user.active = 1
)
OR req.user_id IN (
  SELECT id from user where id in (SELECT approved_employee_id from approver where approver_id = '269') and user.active = 1
))
   AND req.status = 'pending';

返回124条记录。

我通过联接写下面的查询，但不起作用，

SELECT DISTINCT req.*
FROM request req
  LEFT JOIN user u ON u.id = req.user_id AND u.active = 1
  LEFT JOIN team_member team ON team.user_id = u.id AND team.team_id IN ('344', '723')
  LEFT JOIN approver app ON app.approver_id = u.id AND app.approver_id = '269'
AND req.status = 'pending';

返回超过500条记录。

这个联接有两个问题，它包括状态未待决的那些请求。

以下是架构

我有以下表格

tbl_approver = 
id, 
approver_id (FK tbl_user), 
approver_team_id (FK tbl_team), 
approved_employee_id (FK tbl_user)

tbl_team_mambers = 
id, 
team_id (FK), 
user_id (FK)

tble_user = 
id, 
email, 
username
active


tbl_request = 
id, 
user_id, 
status

团队成员：用户是多个团队的成员。
审批人：
- 每个团队都有一个审批人，他也是该团队的成员。
- 无论团队如何，都可以直接批准员工。
请求：用户的库存请求

注意：作为审批人，我可以成为许多团队的成员，但只有批准者一些团队或者也是一些员工。

需要查询：作为审批人，我想要我批准的所有团队的请求。

Answer 1

要获得join的正确结果，您需要为任何连接的“表”返回user_id只有一行。如果只需要所有表中存在的行，请不要使用left。

SELECT req.*
  FROM request req
  JOIN user ON user.id=req.user_id
  JOIN (
        SELECT distinct approved_employee_id as user_id from approver where approver_id = '269'
         UNION
        SELECT distinct user_id FROM team_member team WHERE team.team_id IN ('344', '723')
       ) A ON req.user_id=A.user_id
 where user.active = 1
   AND req.status = 'pending';

或者，如果只需要“真正的桌子”：

SELECT DISTINCT req.*
  FROM request req
  JOIN user u ON u.id = req.user_id AND u.active = 1
  LEFT JOIN team_member team ON team.user_id = u.id AND team.team_id IN ('344', '723')
  LEFT JOIN approver app  ON app.approver_id = u.id AND app.approver_id = '269'
 WHERE req.status = 'pending'
   AND (team.user_id is not null OR app.approver_id is not null)

Answer 2

观看LEFT JOIN语法，此处为visual expression of joins

SELECT DISTINCT req.*
FROM request req
LEFT JOIN user u ON u.id = req.user_id AND u.active = 1
...

这将从request中选择所有不同的记录，并为用户选择JOIN个记录。 join_condition之后的ON只会影响联接关系。

如果LEFT JOIN中的ON或USING部分中的右表没有匹配的行，则将所有列设置为NULL的行用于右表。

Join syntax from Mysql Documentation

如果您确实想使用LEFT JOIN来过滤request的所有记录，请考虑将condition_expr移至WHERE

SELECT DISTINCT req.*
FROM request req
LEFT JOIN user u ON u.id = req.user_id
...
WHERE u.active = 1
AND ...

如果您只需要request满足用户的加入条件，则应考虑使用Join而不是LEFT JOIN。

将子查询转换为连接

2 个答案: