MySQL七大JOIN的具体使用

DROP TABLE IF EXISTS `dept`;
CREATE TABLE `dept` (
`dept_id` int(11) NOT NULL AUTO_INCREMENT,
`dept_name` varchar(30) DEFAULT NULL,
`dept_number` int(11) DEFAULT NULL,
PRIMARY KEY (`dept_id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

INSERT INTO `dept` VALUES (‘1’, ‘AA’, ‘100’);
INSERT INTO `dept` VALUES (‘2’, ‘BB’, ‘200’);
INSERT INTO `dept` VALUES (‘3’, ‘CC’, ‘300’);
INSERT INTO `dept` VALUES (‘4’, ‘DD’, ‘400’);
INSERT INTO `dept` VALUES (‘5’, ‘HH’, ‘500’);

DROP TABLE IF EXISTS `emp`;
CREATE TABLE `emp` (
`emp_id` int(11) NOT NULL AUTO_INCREMENT,
`emp_name` varchar(30) DEFAULT NULL,
`emp_age` int(11) DEFAULT NULL,
`dept_id` int(11) NOT NULL,
PRIMARY KEY (`emp_id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

INSERT INTO `emp` VALUES(‘1’, ‘zhangsan’, ’20’, ‘1’);
INSERT INTO `emp` VALUES(‘2’, ‘lisi’, ’25’, ‘6’);
INSERT INTO `emp` VALUES(‘3’, ‘wangwu’, ’19’, ‘4’);
INSERT INTO `emp` VALUES(‘4’, ‘zhaoliu’, ’29’, ‘5’);
INSERT INTO `emp` VALUES(‘5’, ‘xiaohong’, ’30’, ‘2’);
INSERT INTO `emp` VALUES(‘6’, ‘xiaohu’, ’26’, ‘3’);
INSERT INTO `emp` VALUES(‘7’, ‘zhangle’, ’23’, ‘3’);
INSERT INTO `emp` VALUES(‘8’, ‘qingtian’, ’38’, ‘3’);
INSERT INTO `emp` VALUES(‘9’, ‘xiayutian’, ’36’, ‘2’);
INSERT INTO `emp` VALUES(’10’, ‘fangjia’, ’40’, ‘1’);

SELECT * from emp e LEFT JOIN dept d ON e.dept_id=d.dept_id;

SELECT * from emp e RIGHT JOIN dept d ON e.dept_id=d.dept_id;

SELECT * from emp e INNER JOIN dept d ON e.dept_id=d.dept_id;

SELECT * from emp e LEFT JOIN dept d ON e.dept_id=d.dept_id WHERE d.dept_id is null;

SELECT * from emp e RIGHT JOIN dept d ON e.dept_id=d.dept_id WHERE e.dept_id is null;

SELECT * from emp e LEFT JOIN dept d ON e.dept_id=d.dept_id UNION SELECT * FROM emp e RIGHT JOIN dept d ON e.dept_id=d.dept_id;

SELECT * from emp e LEFT JOIN dept d ON e.dept_id=d.dept_id WHERE d.dept_id is null UNION SELECT * FROM emp e RIGHT JOIN dept d ON e.dept_id=d.dept_id WHERE e.dept_id is null;