TSQL之JOIN（连接）彻底理解

T-SQL之JOIN彻底理解

本文不解释，欢迎提问解答，谢谢。直接上代码：

?

--测试数据建立

Create TABLE JOIN_TEST(

COLA INT,

COLB INT

)

 

GO

INSERT INTO JOIN_TEST

SELECT 1,1

 

INSERT INTO JOIN_TEST

SELECT 1,1

 

GO

--测试数据建立完毕

 

SELECT * FROM JOIN_TEST

/*

 

COLA        COLB

----------- -----------

1           1

1           1

 

(2 行受影响)

*/

 

 

SELECT * FROM JOIN_TEST A  CROSS JOIN JOIN_TEST B

/*

COLA        COLB        COLA        COLB

----------- ----------- ----------- -----------

1           1           1           1

1           1           1           1

1           1           1           1

1           1           1           1

 

(4 行受影响)

 

*/

 

 

SELECT * FROM JOIN_TEST A  INNER JOIN  JOIN_TEST B ON A.COLA=B.COLA

/*

COLA        COLB        COLA        COLB

----------- ----------- ----------- -----------

1           1           1           1

1           1           1           1

1           1           1           1

1           1           1           1

(4 行受影响)

 

*/

 

 

SELECT * FROM JOIN_TEST A  LEFT JOIN  JOIN_TEST B ON A.COLA=B.COLA

/*

COLA        COLB        COLA        COLB

----------- ----------- ----------- -----------

1           1           1           1

1           1           1           1

1           1           1           1

1           1           1           1

(4 行受影响)

 

*/

 

SELECT * FROM JOIN_TEST A  LEFT JOIN  JOIN_TEST B ON A.COLA=B.COLA AND A.COLA<>1

/*

COLA        COLB        COLA        COLB

----------- ----------- ----------- -----------

1           1           NULL        NULL

1           1           NULL        NULL

(2 行受影响)

*/

 

SELECT * FROM JOIN_TEST A  LEFT JOIN  JOIN_TEST B ON A.COLA=B.COLA WHERE A.COLA<>1

/*

COLA        COLB        COLA        COLB

----------- ----------- ----------- -----------

 

(0 行受影响)

*/

 

SELECT * FROM JOIN_TEST A  FULL JOIN  JOIN_TEST B ON A.COLA=B.COLA AND A.COLA<>1

/*

COLA        COLB        COLA        COLB

----------- ----------- ----------- -----------

1           1           NULL        NULL

1           1           NULL        NULL

NULL        NULL        1           1

NULL        NULL        1           1

*/

 

SELECT * FROM JOIN_TEST A  FULL JOIN  JOIN_TEST B ON A.COLA=B.COLA where A.COLA<>1

/*

COLA        COLB        COLA        COLB

----------- ----------- ----------- -----------

 

(0 行受影响)

*/

分类: SQL SERVER T-TQL