Question

我的ms sql中有这种查询。

SELECT 
    OdeaMainDataBase.dbo.ItemChoicesTable.*,
    CASE
       WHEN EXISTS(SELECT * FROM StudentTestTablefromRemark 
                   WHERE StudID = @studId AND ExamID = @examId 
                     AND ItemBankID = @itemBankId 
                     AND ChoiceID = OdeaMainDataBase.dbo.ItemChoicesTable.ChoiceID) 
          THEN 'True' 
          ELSE 'False' 
    END AS isAnswered
FROM 
    OdeaMainDataBase.dbo.ItemChoicesTable
WHERE
    ItemBankID = @itemBankId

我观察到我所做的CASE语句导致我的查询运行缓慢。当我删除CASE时，它运行得很快，但我的输出需要这种情况。

这是我想要显示的结构

项目选择表

ItemBankID   ChoiceID    ChoiceLetter
--------------------------------------
1            1           A
1            2           B
1            3           C
2            4           A
2            5           B
2            6           C

学生答案表

ItemBankID   ChoiceID    ChoiceLetter   StudentId
-------------------------------------------------
1            2           B              123
2            6           C              123

所需输出

ItemBankID   ChoiceID    ChoiceLetter    IsAnswered
----------------------------------------------------
1            1           A               False
1            2           B               True
1            3           C               False
2            4           A               False
2            5           B               False
2            6           C               True

我希望在不减慢程序速度的情况下实现输出。

任何想法都会对我有用。

非常感谢

Answer 1

试试这个

SELECT i.*,
       CASE
         WHEN s.ChoiceID IS NULL THEN 'False'
         ELSE 'True'
       END
FROM   OdeaMainDataBase.dbo.ItemChoicesTable i
       LEFT OUTER JOIN StudentTestTablefromRemark s
                    ON s.ChoiceID = i.ChoiceID
                       AND s.ItemBankID = i.ItemBankID
                       AND s.StudID = @studId
                       AND s.ExamID = @examId
WHERE  i.ItemBankID = @itemBankId

Answer 2

尝试此查询

SELECT OdeaMainDataBase.dbo.ItemChoicesTable.*,
ISNULL(a,'False') as isAnswered
FROM OdeaMainDataBase.dbo.ItemChoicesTable 
left outer join(Select 'True' as a,ChoiceID FROM StudentTestTablefromRemark 
Where StudID=@studId AND ExamID=@examId AND ItemBankID=@itemBankId )b on b.ChoiceID=OdeaMainDataBase.dbo.ItemChoicesTable.ChoiceID
Where ItemBankID = @itemBankId

如何让我的MS SQL Server查询运行得更快？

2 个答案: