SQL-关联查询

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