T_A A表 T_B B标，id为表与表相关联的字段`
创建相关表结构
CREATE TABLE Table_B( id INT(2), serNum VARCHAR(10) ); CREATE TABLE Table_A( id INT(2), serNum VARCHAR(10) ); INSERT INTO table_a (id, serNum) VALUES (1,'A000101'),(2,'A000102'),(3,'A000103'),(5,'A000104'),(8,'A000105'),(4,'A000106'); INSERT INTO table_b (id, serNum) VALUES (1,'B000201'),(2,'B000202'),(3,'B000203'),(6,'B000204'),(7,'B000205'),(9,'B000206'); 
Table_A
id serNum
------ ---------
1 A000100
2 A000102
3 A000103
5 A000104
8 A000105
4 A000106
Table_B
id serNum
------ ---------
1 B000201
2 B000202
3 B000203
6 B000204
7 B000205
9 B000206
1. inner join 内连接查询
SELECT a.*,b.*
FROM table_a a
INNER JOIN table_b b
ON a.id=b.id查询结果：
id serNum id serNum
------ ------- ------ ---------
1 A000100 1 B000201
2 A000102 2 B000202
3 A000103 3 B000203
2. left join 左关联查询
以左表作为基础表去关联右表，查询的结果为左表的子集
SELECT a.*,b.*
FROM table_a a
LEFT JOIN table_b b
ON a.id=b.id查询结果：
id serNum id serNum
------ ------- ------ ---------
1 A000100 1 B000201
2 A000102 2 B000202
3 A000103 3 B000203
5 A000104 (NULL) (NULL)
8 A000105 (NULL) (NULL)
4 A000106 (NULL) (NULL)
3.right join 右关联查询
以右表作为基础表去关联左表，查询的结果为右表的子集
SELECT a.*,b.*
FROM table_a a
RIGHT JOIN table_b b
ON a.id=b.id查询结果：
id serNum id serNum
------ ------- ------ ---------
1 A000100 1 B000201
2 A000102 2 B000202
3 A000103 3 B000203
(NULL) (NULL) 6 B000204
(NULL) (NULL) 7 B000205
(NULL) (NULL) 9 B000206
4.左连接-内连接
取左表的部分集合，但又不存在右表中
SELECT a.*,b.*
FROM table_a a
LEFT JOIN table_b b
ON a.id=b.id WHERE b.id IS NULL查询结果：
id serNum id serNum
------ ------- ------ --------
5 A000104 (NULL) (NULL)
8 A000105 (NULL) (NULL)
4 A000106 (NULL) (NULL)
5. 右连接-内连接
取有表的部分数据，但又不存在左表中
SELECT a.*,b.*
FROM table_a a
RIGHT JOIN table_b b
ON a.id=b.id WHERE a.id IS NULL查询结果：
id serNum id serNum
------ ------ ------ ---------
(NULL) (NULL) 6 B000204
(NULL) (NULL) 7 B000205
(NULL) (NULL) 9 B000206
转载于:https://www.cnblogs.com/cwind/p/11062440.html