关于SQL中join的各种用法总结
时间:2019-4-17 20:58 作者:admin 分类: 技术文章
首先声明:文章来源于国外的 codeproject 我这里只是由于复习SQL的时候需要就Google搜索[可以用我个人搭建的Google搜索供大家搜索文章学习使用]了一下,找到这篇文章,再次做个简单的记录同时也方便以后的有缘人,如有侵权的地方还请来信注明,感谢原文的作者的勤劳付出,留下如此详细全面的关于SQL的join的用法。
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我们先用一张图来看一下 LEFT JOIN、RIGHT JOIN、INNER JOIN、OUTER JOIN 等七种 join 相关的用法:
下面分开说明这七种用法,先说第一种:
1.INNER JOIN(内连接)
这是最简单,最容易理解的Join,也是最常见的。此查询将返回左表(表A)中右表(表B)中都具有匹配记录的所有记录(共同拥有的相同的部分)。此Join用法的代码大致如下:
SELECT <select_list> FROM Table_A A INNER JOIN Table_B B ON A.Key = B.Key
2.LEFT JOIN
(左连接)
LEFT JOIN 关键字会从左表 (table_name1) 那里返回所有的行,即使在右表 (table_name2) 中没有匹配的行。此Join用法的代码大致如下:
SELECT <select_list> FROM Table_A A LEFT JOIN Table_B B ON A.Key = B.Key
3.RIGHT JOIN
(右连接)
RIGHT JOIN 关键字从右表(table2)返回所有的行,即使左表(table1)中没有匹配。如果左表中没有匹配,则结果为 NULL。此Join用法的代码大致如下:
SELECT <select_list> FROM Table_A A RIGHT JOIN Table_B B ON A.Key = B.Key
4.OUTER JOIN
(外连接)
FULL OUTER JOIN 关键字只要左表(table1)和右表(table2)其中一个表中存在匹配,则返回行. FULL OUTER JOIN 关键字结合了 LEFT JOIN 和 RIGHT JOIN 的结果。此Join用法的代码大致如下:
SELECT <select_list> FROM Table_A A FULL OUTER JOIN Table_B B ON A.Key = B.Key
5.LEFT JOIN EXCLUDING INNER JOIN
(左连接-内连接)
此查询将返回左表(表A)中与右表(表B)中的任何记录都不匹配的所有记录。此Join的编写如下:
SELECT <select_list> FROM Table_A A LEFT JOIN Table_B B ON A.Key = B.Key WHERE B.Key IS NULL
6.RIGHT JOIN EXCLUDING INNER JOIN
(右连接-内连接)
此查询将返回右表(表B)中与左表(表A)中的任何记录都不匹配的所有记录。此Join的编写如下:
SELECT <select_list> FROM Table_A A RIGHT JOIN Table_B B ON A.Key = B.Key WHERE A.Key IS NULL
7.OUTER JOIN EXCLUDING INNER JOIN
(外连接-内连接)
此查询将返回左表(表A)中的所有记录以及右表(表B)中都不匹配的所有记录。我还没有需要使用这种类型的Join,但是其他的类型,我经常使用。此Join的编写如下:
SELECT <select_list> FROM Table_A A FULL OUTER JOIN Table_B B ON A.Key = B.Key WHERE A.Key IS NULL OR B.Key IS NULL
下面举一些例子:
TABLE_A PK Value ---- ---------- 1 FOX 2 COP 3 TAXI 6 WASHINGTON 7 DELL 5 ARIZONA 4 LINCOLN 10 LUCENT TABLE_B PK Value ---- ---------- 1 TROT 2 CAR 3 CAB 6 MONUMENT 7 PC 8 MICROSOFT 9 APPLE 11 SCOTCH这七种连接方式的结果如下所示:
-- INNER JOIN SELECT A.PK AS A_PK, A.Value AS A_Value, B.Value AS B_Value, B.PK AS B_PK FROM Table_A A INNER JOIN Table_B B ON A.PK = B.PK A_PK A_Value B_Value B_PK ---- ---------- ---------- ---- 1 FOX TROT 1 2 COP CAR 2 3 TAXI CAB 3 6 WASHINGTON MONUMENT 6 7 DELL PC 7 (5 row(s) affected)
-- LEFT JOIN SELECT A.PK AS A_PK, A.Value AS A_Value, B.Value AS B_Value, B.PK AS B_PK FROM Table_A A LEFT JOIN Table_B B ON A.PK = B.PK A_PK A_Value B_Value B_PK ---- ---------- ---------- ---- 1 FOX TROT 1 2 COP CAR 2 3 TAXI CAB 3 4 LINCOLN NULL NULL 5 ARIZONA NULL NULL 6 WASHINGTON MONUMENT 6 7 DELL PC 7 10 LUCENT NULL NULL (8 row(s) affected)
-- RIGHT JOIN SELECT A.PK AS A_PK, A.Value AS A_Value, B.Value AS B_Value, B.PK AS B_PK FROM Table_A A RIGHT JOIN Table_B B ON A.PK = B.PK A_PK A_Value B_Value B_PK ---- ---------- ---------- ---- 1 FOX TROT 1 2 COP CAR 2 3 TAXI CAB 3 6 WASHINGTON MONUMENT 6 7 DELL PC 7 NULL NULL MICROSOFT 8 NULL NULL APPLE 9 NULL NULL SCOTCH 11 (8 row(s) affected)
-- OUTER JOIN SELECT A.PK AS A_PK, A.Value AS A_Value, B.Value AS B_Value, B.PK AS B_PK FROM Table_A A FULL OUTER JOIN Table_B B ON A.PK = B.PK A_PK A_Value B_Value B_PK ---- ---------- ---------- ---- 1 FOX TROT 1 2 COP CAR 2 3 TAXI CAB 3 6 WASHINGTON MONUMENT 6 7 DELL PC 7 NULL NULL MICROSOFT 8 NULL NULL APPLE 9 NULL NULL SCOTCH 11 5 ARIZONA NULL NULL 4 LINCOLN NULL NULL 10 LUCENT NULL NULL (11 row(s) affected)
-- LEFT EXCLUDING JOIN SELECT A.PK AS A_PK, A.Value AS A_Value, B.Value AS B_Value, B.PK AS B_PK FROM Table_A A LEFT JOIN Table_B B ON A.PK = B.PK WHERE B.PK IS NULL A_PK A_Value B_Value B_PK ---- ---------- ---------- ---- 4 LINCOLN NULL NULL 5 ARIZONA NULL NULL 10 LUCENT NULL NULL (3 row(s) affected)
-- RIGHT EXCLUDING JOIN SELECT A.PK AS A_PK, A.Value AS A_Value, B.Value AS B_Value, B.PK AS B_PK FROM Table_A A RIGHT JOIN Table_B B ON A.PK = B.PK WHERE A.PK IS NULL A_PK A_Value B_Value B_PK ---- ---------- ---------- ---- NULL NULL MICROSOFT 8 NULL NULL APPLE 9 NULL NULL SCOTCH 11 (3 row(s) affected)
-- OUTER EXCLUDING JOIN SELECT A.PK AS A_PK, A.Value AS A_Value, B.Value AS B_Value, B.PK AS B_PK FROM Table_A A FULL OUTER JOIN Table_B B ON A.PK = B.PK WHERE A.PK IS NULL OR B.PK IS NULL A_PK A_Value B_Value B_PK ---- ---------- ---------- ---- NULL NULL MICROSOFT 8 NULL NULL APPLE 9 NULL NULL SCOTCH 11 5 ARIZONA NULL NULL 4 LINCOLN NULL NULL 10 LUCENT NULL NULL (6 row(s) affected)注:原文连接:https://www.codeproject.com/Articles/33052/Visual-Representation-of-SQL-Joins