INNER LEFT RIGHT JOIN

CREATE TABLE `a` (
  `a1` VARCHAR(10) DEFAULT NULL,
  `b1` VARCHAR(10) DEFAULT NULL,
  `c1` VARCHAR(10) DEFAULT NULL
) ENGINE=INNODB DEFAULT CHARSET=utf8

CREATE TABLE `b` (
  `a2` VARCHAR(10) DEFAULT NULL,
  `b2` VARCHAR(10) DEFAULT NULL
) ENGINE=INNODB DEFAULT CHARSET=utf8

 创建出表，表内数据如下：

SQL语句执行结果图片在语句的下方

#inner join
SELECT A.*,B.* 
FROM a INNER JOIN B ON a.a1=b.a2

 

#left join
SELECT A.*,B.* 
FROM a LEFT OUTER JOIN b ON a.a1 = b.a2

 

#right join
SELECT A.*,B.* 
FROM a RIGHT OUTER JOIN b ON a.a1 = b.a2

#full outer join union
SELECT A.*,B.* 
FROM a LEFT OUTER JOIN b ON a.a1 = b.a2
UNION
SELECT A.*,B.* 
FROM a RIGHT OUTER JOIN b ON a.a1 = b.a2

 

SELECT A.*, B.* FROM A,B

 

SELECT A.*,B.* 
FROM a JOIN b ON a.a1 = b.a2

 默认是inner join