TSQL查询通过连接两个表来获取不同WHERE子句的同一列值的差异

Question

Below is the sample query which gives the rating by employee and manager from two different tables.

SELECT pr.[task_id],
       pr.[user_rating],ts.[title]
FROM [dbo].[rpt_task] ts
      INNER JOIN [dbo].[rpt_review] pr ON ts.[task_id] = pr.[task_id]
WHERE ts.[culture_id] = 1

Now, I am trying to draft the query where the result be like

Sample Desired Output - [ variance being(user_rating of 'Manager review' - user_rating of 'self_Review')

task_id   variance
6095      0

I have tried as

SELECT pr.[task_id],
       ((SELECT pr.[user_rating]
         FROM [dbo].[rpt_task] ts
              INNER JOIN [dbo].[rpt_review] pr ON ts.[task_id] = pr.[task_id]
         WHERE ts.[title] = 'Manager Review') -
        (SELECT pr.[user_rating]
         FROM [dbo].[rpt_task] ts
              INNER JOIN [dbo].[rpt_review] pr ON ts.[task_id] = pr.[task_id]
         WHERE ts.[title] = 'Self Review'))
FROM [dbo].[rpt_task] ts
      INNER JOIN [dbo].[rpt_review] pr ON ts.[task_id] = pr.[task_id]  
WHERE ts.[culture_id] = 1
GROUP BY pr.[task_id]

Answer 1

ASSUMPTION : You didn't provide the table structure of the underlying tables, hence I'm assuming that the rpt_review table doesn't need to be joined twice, as there's one record there, and one record for each reviewer in the rpt_task table.
Please correct me if this assumption isn't correct.

You'll need to self-join the table in order to get both the manager and the self reviews. I've joined both of them to the rpt_review table and did the math as you were trying to do.

Sample Code:

SELECT 
     pr.[task_id]
    ,ts_manager.[user_rating] - ts_self.[user_rating] AS Variance
FROM [dbo].[rpt_task] ts_self
INNER JOIN [dbo].[rpt_review] pr ON ts.[task_id] = pr.[task_id]
INNER JOIN [dbo].[rpt_task] ts_manager ON ts_self.culture_id = ts_manager.culture_id
WHERE ts_self.[culture_id] = 1
AND ts_self.[title] = 'Self Review'
AND ts_manager.[title] = 'Manager Review';