MySQL高级 第4章SQL预热
1. 常见的Join查询图
2. Join示例
2.1 建表语句
CREATE TABLE `t_dept` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`deptName` VARCHAR(30) DEFAULT NULL,
`address` VARCHAR(40) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=INNODB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
CREATE TABLE `t_emp` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`name` VARCHAR(20) DEFAULT NULL,
`age` INT(3) DEFAULT NULL,
`deptId` INT(11) DEFAULT NULL,
empno int not null,
PRIMARY KEY (`id`),
KEY `idx_dept_id` (`deptId`)
#CONSTRAINT `fk_dept_id` FOREIGN KEY (`deptId`) REFERENCES `t_dept` (`id`)
) ENGINE=INNODB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
INSERT INTO t_dept(deptName,address) VALUES('华山','华山');
INSERT INTO t_dept(deptName,address) VALUES('丐帮','洛阳');
INSERT INTO t_dept(deptName,address) VALUES('峨眉','峨眉山');
INSERT INTO t_dept(deptName,address) VALUES('武当','武当山');
INSERT INTO t_dept(deptName,address) VALUES('明教','光明顶');
INSERT INTO t_dept(deptName,address) VALUES('少林','少林寺');
INSERT INTO t_emp(NAME,age,deptId,empno) VALUES('风清扬',90,1,100001);
INSERT INTO t_emp(NAME,age,deptId,empno) VALUES('岳不群',50,1,100002);
INSERT INTO t_emp(NAME,age,deptId,empno) VALUES('令狐冲',24,1,100003);
INSERT INTO t_emp(NAME,age,deptId,empno) VALUES('洪七公',70,2,100004);
INSERT INTO t_emp(NAME,age,deptId,empno) VALUES('乔峰',35,2,100005);
INSERT INTO t_emp(NAME,age,deptId,empno) VALUES('灭绝师太',70,3,100006);
INSERT INTO t_emp(NAME,age,deptId,empno) VALUES('周芷若',20,3,100007);
INSERT INTO t_emp(NAME,age,deptId,empno) VALUES('张三丰',100,4,100008);
INSERT INTO t_emp(NAME,age,deptId,empno) VALUES('张无忌',25,5,100009);
INSERT INTO t_emp(NAME,age,deptId,empno) VALUES('韦小宝',18,null,100010);
2.2 案例
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1.所有有门派人员的信息（要求显示门派名称） |
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SELECT e.`name`,d.`deptName` FROM t_emp e INNER JOIN t_dept d ON e.`deptId`=d.`id`; |
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2. 列出所有人员及其门派信息 |
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SELECT e.`name`,d.`deptName` FROM t_emp e LEFT JOIN t_dept d ON e.`deptId`=d.`id`; |
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3. 列出所有门派 |
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SELECT * FROM t_dept; |
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4. 所有无门派人士 |
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SELECT * FROM t_emp WHERE deptId IS NULL; |
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5. 所有无人门派 |
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SELECT d.* FROM t_dept d LEFT JOIN t_emp e ON d.`id`=e.`deptId` WHERE e.`deptId` IS NULL; |
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6. 所有人员和门派的对应关系 |
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SELECT * FROM t_emp e LEFT JOIN t_dept d ON e.`deptId`=d.`id` UNION SELECT * FROM t_emp e RIGHT JOIN t_dept d ON e.`deptId`=d.`id`; |
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7. 所有没有入门派的人员和没人入的门派 |
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SELECT * FROM t_emp e LEFT JOIN t_dept d ON e.`deptId`=d.`id` WHERE e.deptId IS NULL UNION SELECT * FROM t_dept d LEFT JOIN t_emp e ON d.`id`=e.`deptId` WHERE e.`deptId` IS NULL; |
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8. 添加CEO字段 ALTER TABLE `t_dept` add CEO INT(11) ; update t_dept set CEO=2 where id=1; update t_dept set CEO=4 where id=2; update t_dept set CEO=6 where id=3; update t_dept set CEO=8 where id=4; update t_dept set CEO=9 where id=5; |
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8.1 求各个门派对应的掌门人名称 |
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SELECT d.deptName,e.name FROM t_dept d LEFT JOIN t_emp e ON d.ceo=e.id |
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8.2求所有当上掌门人的平均年龄 |
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SELECT AVG(e.age) FROM t_dept d LEFT JOIN t_emp e ON d.ceo=e.id |
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8.3求所有人物对应的掌门名称 |
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SELECT ed.name '人物',c.name '掌门' FROM (SELECT e.name,d.ceo from t_emp e LEFT JOIN t_dept d on e.deptid=d.id) ed LEFT JOIN t_emp c on ed.ceo= c.id; |
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SELECT e.name '人物',tmp.name '掌门' FROM t_emp e LEFT JOIN (SELECT d.id did,e.name FROM t_dept d LEFT JOIN t_emp e ON d.ceo=e.id)tmp ON e.deptId=tmp.did; |
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SELECT e1.name '人物',e2.name '掌门' FROM t_emp e1 LEFT JOIN t_dept d on e1.deptid = d.id LEFT JOIN t_emp e2 on d.ceo = e2.id ;
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