Question

我有以下表格及其插入脚本：

    DECLARE @A TABLE
    (
      [ID] INT IDENTITY,
      [SID] INT 
    )


DECLARE @EP TABLE
    (
      [SID] INT ,
      [RID] INT ,
      [HR] INT
    )

DECLARE  @XR TABLE
    (
      [SID] INT ,
      [RID] INT ,
      [UID] INT
    )

DECLARE @SR TABLE
    (
      [RID] INT ,
      [RNAME] VARCHAR(10),
      [SID] INT
    )


INSERT INTO @A
SELECT 1 UNION 
SELECT 2


INSERT INTO  @EP
SELECT 1, 1, 1 UNION   
SELECT 1, 2, 1 UNION
SELECT 1, 3, 1 UNION
SELECT 2, 4, 1 UNION
SELECT 2, 5, 1 UNION
SELECT 2, 6, 1 

INSERT INTO  @XR
SELECT 1, 1, 1 UNION   
SELECT 1, 2, 1 UNION
SELECT 1, 2, 2 UNION
SELECT 2, 4, 1 UNION
SELECT 2, 5, 2 

INSERT INTO @SR
SELECT 1,'Apple', 1 UNION
SELECT 2,'Mango', 1 UNION
SELECT 3,'Banana',1 UNION
SELECT 4,'Apple', 2 UNION
SELECT 5,'Mango', 2 UNION
SELECT 6,'Banana',2

当我运行以下SQL查询时，我得到两个输出行，这很好：

DECLARE @UD INT 
SET @UD=1

SELECT * FROM @A A
WHERE EXISTS(
    SELECT 1                      
    FROM   @EP [EP]                      
    INNER JOIN @XR XR ON [EP].SID = A.SID 
    WHERE  [EP].SID = A.SID                     
    AND [EP].RID = XR.RID  
    AND [EP].[HR] = 1                      
    AND XR.UID = @UD
)
--OUTPUT
--ID          SID
------------- -----------
--1           1
--2           2

但是当我使用“@ UD = 3”运行上述查询时，我没有记录。我想在这里放一个条件连接，它应该是这样的：

SELECT * FROM @A A
--IF((SELECT COUNT(*) FROM @XR XR WHERE XR.XR=A.SID)>0) 
WHERE EXISTS(
    SELECT 1                      
    FROM   @EP [EP]                      
    INNER JOIN @XR XR ON [EP].SID = A.SID 
    WHERE  [EP].SID = A.SID                     
    AND [EP].RID = XR.RID  
    AND [EP].[HR] = 1                      
    AND XR.UID = @UD
)
--ELSE
WHERE EXISTS(
    SELECT 1                      
    FROM   @EP [EP]                      
    INNER JOIN @SR SR ON SR.SID = A.SID 
    WHERE  [EP].SID = A.SID                     
    AND [EP].RID = SR.RID  
    AND [EP].[HR] = 1                      
    AND SR.[RNAME] = 'Banana'
)

abover查询应返回@UID 1和3的两行，即如果没有找到特定uid的@XR记录，则应该转到else循环。你能帮我解决这个问题吗？我不想在这里使用 union ，并希望在 SINGLE 查询中执行相同的操作，仅使用 join 中的条件而不是写外部if和else循环。

Answer 1

SELECT * FROM @A A
WHERE ((SELECT COUNT(*) FROM @XR XR WHERE XR.XR=A.SID)=0 AND EXISTS(
    SELECT 1                      
    FROM   @EP [EP]                      
    INNER JOIN @XR XR ON [EP].SID = A.SID 
    WHERE  [EP].SID = A.SID                     
    AND [EP].RID = XR.RID  
    AND [EP].[HR] = 1                      
    AND XR.UID = @UD
)) OR ((SELECT COUNT(*) FROM @XR XR WHERE XR.XR=A.SID)!=0 AND EXISTS(
    SELECT 1                      
    FROM   @EP [EP]                      
    INNER JOIN @SR SR ON SR.SID = A.SID 
    WHERE  [EP].SID = A.SID                     
    AND [EP].RID = SR.RID  
    AND [EP].[HR] = 1                      
    AND SR.[RNAME] = 'Banana'
))

即。只需将两者合并为一个简单的布尔值即可。您可能不需要第二个COUNT（*）查询BTW。

Answer 2

如果我正确理解要求，应该这样做：

SELECT DISTINCT
    A.* 
FROM @A AS A
JOIN @EP AS EP ON A.SID = EP.SID
LEFT JOIN @XR AS XR ON EP.RID = XR.RID
LEFT JOIN @SR AS SR ON  SR.SID = A.SID
WHERE EP.HR = 1
    AND (XR.UID = @UD OR RNAME IS NOT NULL)

如何进行条件SQL连接

2 个答案: