MySQL查询 内连接

测试数据：
suppliers

CREATE TABLE suppliers(
s_id INT NOT NULL AUTO_INCREMENT,
s_name CHAR(50) NOT NULL,
s_city CHAR(10) NULL,
s_zip CHAR(10) NULL,
s_call CHAR(50) NOT NULL,
PRIMARY KEY(s_id)
);
INSERT INTO suppliers(s_id, s_name,s_city,  s_zip, s_call)
VALUES(101,'FastFruit Inc.','Tianjin','300000','48075'),
(NULL,'LT Supplies','Chongqing','400000','44333'),
(NULL,'ACME','Shanghai','200000','90046'),
(NULL,'FNK Inc.','Zhongshan','528437','11111'),
(NULL,'Good Set','Taiyuang','030000', '22222'),
(NULL,'Just Eat Ours','Beijing','010', '45678'),
(NULL,'DK Inc.','Zhengzhou','450000', '33332');

fruits

CREATE TABLE fruits
(
f_id    char(10)     	NOT NULL,
s_id    INT        	NOT NULL,
f_name  char(255)  	NOT NULL,
f_price decimal(8,2)  	NOT NULL,
PRIMARY KEY(f_id) 
); 
 
 
 INSERT INTO fruits (f_id, s_id, f_name, f_price)
     VALUES('a1', 101,'apple',5.2),
     ('b1',101,'blackberry', 10.2),
     ('bs1',102,'orange', 11.2),
     ('bs2',105,'melon',8.2),
     ('t1',102,'banana', 10.3),
     ('t2',102,'grape', 5.3),
     ('o2',103,'coconut', 9.2),
     ('c0',101,'cherry', 3.2),
     ('a2',103, 'apricot',2.2),
     ('l2',104,'lemon', 6.4),
     ('b2',104,'berry', 7.6),
     ('m1',106,'mango', 15.6),
     ('m2',105,'xbabay', 2.6),
     ('t4',107,'xbababa', 3.6),
     ('m3',105,'xxtt', 11.6),
     ('b5',107,'xxxx', 3.6);

表结构：
fruit

f_id      s_id  f_name      f_price  
------  ------  ----------  ---------
a1         101  apple       5.20     
a2         103  apricot     2.20     
b1         101  blackberry  10.20    
b2         104  berry       7.60     
b5         107  xxxx        3.60     
bs1        102  orange      11.20    
bs2        105  melon       8.20     
c0         101  cherry      3.20     
l2         104  lemon       6.40     
m1         106  mango       15.60    
m2         105  xbabay      2.60     
m3         105  xxtt        11.60    
o2         103  coconut     9.20     
t1         102  banana      10.30    
t2         102  grape       5.30     
t4         107  xbababa     3.60     

suppliers

  s_id  s_name          s_city     s_zip   s_call  
------  --------------  ---------  ------  --------
   101  FastFruit Inc.  Tianjin    300000  48075   
   102  LT Supplies     Chongqing  400000  44333   
   103  ACME            Shanghai   200000  90046   
   104  FNK Inc.        Zhongshan  528437  11111   
   105  Good Set        Taiyuang   030000  22222   
   106  Just Eat Ours   Beijing    010     45678   
   107  DK Inc.         Zhengzhou  450000  33332  

• 内连接查询

SELECT suppliers.`s_id`,s_name,f_name,f_price
FROM fruits,suppliers
WHERE fruits.`s_id`=suppliers.`s_id`;

因为 fruits 表 和 suppliers表 中有相同的字段 s_id，因此在比较的时候，需要完全限定表名（格式为 “表名,列名”），如果只给出s_id,MySQL将不知道指的是哪一个，并返回错误信息。

- inner join

SELECT suppliers.`s_id`,s_name,f_name,f_price
FROM fruits inner join suppliers
on fruits.`s_id`=suppliers.`s_id`;

查询供应 f_id='a1’的水果商提供的水果种类 及 水果供应商的姓名

select f.`f_name`,s.`s_name` 
from fruits as f inner join suppliers as s on f.`s_id`=s.`s_id` 
where f.`s_id`=(select s_id from fruits as f where f.`f_id`='a1')；

inner join XXXX on XXXX where XXXX

- 自连接
查询供应 f_id='a1’的水果商提供的水果种类

select  f.`f_name` from fruits as f , fruits as r  
where f.`s_id`=r.s_id and r.f_id='a1';

附注：select 子查询

SELECT f.`f_name`
 FROM fruits AS f  
 WHERE f.`s_id`=(SELECT s_id FROM fruits AS f WHERE f.`f_id`='a1')