Sql交叉条件

Question

我想知道我们是否可以做有条件的交叉.theres是somes查询,但结果是错误的(总是空的).我写下应该得到什么.

DECLARE @CAN_USE_TABLE1 BIT
DECLARE @CAN_USE_TABLE2 BIT
DECLARE @CAN_USE_TABLE3 BIT
DECLARE @CAN_USE_TABLE4 BIT

DECLARE @TABLE1 AS TABLE ( ABC INT ) -- values will be 1,2,3
DECLARE @TABLE2 AS TABLE ( ABC INT ) -- values will be 1,2
DECLARE @TABLE3 AS TABLE ( ABC INT ) --EMPTY TABLE
DECLARE @TABLE4 AS TABLE ( ABC INT ) --EMPTY TABLE
INSERT INTO @TABLE1 VALUES (1)
INSERT INTO @TABLE1 VALUES (2)
INSERT INTO @TABLE1 VALUES (3)
INSERT INTO @TABLE2 VALUES (1)
INSERT INTO @TABLE2 VALUES (2)

SET @CAN_USE_TABLE1 = 1
SET @CAN_USE_TABLE2 = 1
SET @CAN_USE_TABLE3 = 1
SET @CAN_USE_TABLE4 = 0

SELECT ABC FROM @TABLE1 WHERE @CAN_USE_TABLE1 = 1
INTERSECT
SELECT ABC FROM @TABLE2 WHERE @CAN_USE_TABLE2 = 1
INTERSECT 
SELECT ABC FROM @TABLE3 WHERE @CAN_USE_TABLE3 = 1
INTERSECT
SELECT ABC FROM @TABLE4 WHERE @CAN_USE_TABLE4 = 1

--RESULT SHOULD BE :
--  NO RESULT
--
--  BECAUSE, AT THIS STAGE, TABLE1 AND TABLE2 AND TABLE3 SHOULD BE INTERSECTED. AND BECAUSE TABLE3 IS EMPTY, THE RESULT IS EMPTY.

SET @CAN_USE_TABLE1 = 1
SET @CAN_USE_TABLE2 = 1
SET @CAN_USE_TABLE3 = 0
SET @CAN_USE_TABLE4 = 0

SELECT ABC FROM @TABLE1 WHERE @CAN_USE_TABLE1 = 1
INTERSECT
SELECT ABC FROM @TABLE2 WHERE @CAN_USE_TABLE2 = 1
INTERSECT 
SELECT ABC FROM @TABLE3 WHERE @CAN_USE_TABLE3 = 1
INTERSECT
SELECT ABC FROM @TABLE4 WHERE @CAN_USE_TABLE4 = 1

--RESULT SHOULD BE :
--  1
--  2
--
--  BECAUSE, AT THIS STAGE, TABLE1 AND TABLE2 SHOULD BE INTERSECTED

SET @CAN_USE_TABLE1 = 0
SET @CAN_USE_TABLE2 = 1
SET @CAN_USE_TABLE3 = 0
SET @CAN_USE_TABLE4 = 0

SELECT ABC FROM @TABLE1 WHERE @CAN_USE_TABLE1 = 1
INTERSECT
SELECT ABC FROM @TABLE2 WHERE @CAN_USE_TABLE2 = 1
INTERSECT 
SELECT ABC FROM @TABLE3 WHERE @CAN_USE_TABLE3 = 1
INTERSECT
SELECT ABC FROM @TABLE4 WHERE @CAN_USE_TABLE4 = 1

--RESULT SHOULD BE :
--  1
--  2
--
--  BECAUSE, AT THIS STAGE, ONLY TABLE 2 SHOULD BE USED

Answer 1

与任何其他集合相结合的空集合INTERSECT将始终为空。这就像乘以 0。你总是得到 0。

Conditional INTERSECTing 将需要动态查询或临时表，如下所示：

初始化

DECLARE @CAN_USE_TABLE1 BIT
DECLARE @CAN_USE_TABLE2 BIT
DECLARE @CAN_USE_TABLE3 BIT
DECLARE @CAN_USE_TABLE4 BIT

DECLARE @TABLE1 AS TABLE ( ABC INT )
DECLARE @TABLE2 AS TABLE ( ABC INT )
DECLARE @TABLE3 AS TABLE ( ABC INT )
DECLARE @TABLE4 AS TABLE ( ABC INT )
DECLARE @RESULT AS TABLE ( ABC INT ) --Adding this result table
INSERT INTO @TABLE1 VALUES (1)
INSERT INTO @TABLE1 VALUES (2)
INSERT INTO @TABLE1 VALUES (3)
INSERT INTO @TABLE2 VALUES (1)
INSERT INTO @TABLE2 VALUES (2)

SET @CAN_USE_TABLE1 = 1
SET @CAN_USE_TABLE2 = 1
SET @CAN_USE_TABLE3 = 0
SET @CAN_USE_TABLE4 = 0

加工

INSERT INTO @RESULT
SELECT ABC FROM @TABLE1 WHERE @CAN_USE_TABLE1=1 UNION
SELECT ABC FROM @TABLE2 WHERE @CAN_USE_TABLE2=1 UNION
SELECT ABC FROM @TABLE3 WHERE @CAN_USE_TABLE3=1 UNION
SELECT ABC FROM @TABLE4 WHERE @CAN_USE_TABLE4=1

DELETE r FROM @RESULT r
WHERE NOT EXISTS(SELECT 1 FROM @TABLE1 WHERE ABC=r.ABC)
AND @CAN_USE_TABLE1=1;

DELETE r FROM @RESULT r
WHERE NOT EXISTS(SELECT 1 FROM @TABLE2 WHERE ABC=r.ABC)
AND @CAN_USE_TABLE2=1;

DELETE r FROM @RESULT r
WHERE NOT EXISTS(SELECT 1 FROM @TABLE3 WHERE ABC=r.ABC)
AND @CAN_USE_TABLE3=1;

DELETE r FROM @RESULT r
WHERE NOT EXISTS(SELECT 1 FROM @TABLE4 WHERE ABC=r.ABC)
AND @CAN_USE_TABLE4=1;

SELECT * FROM @RESULT;

结果

1
2