MySQL高级---索引优化分析(二、join查询练习)

1、建表Sql

CREATE TABLE`tbl_dept`(
`id`INT(11) NOT NULL AUTO_INCREMENT,
`deptName`VARCHAR(30) DEFAULT NULL,
`locAdd`VARCHAR(40) DEFAULT NULL,
PRIMARY KEY (`id`)
)ENGINE=INNODB AUTO_INCREMENT=1 DEFAULT CHARSET=UTF8;

CREATE TABLE`tbl_emp`(
`id`INT(11) NOT NULL AUTO_INCREMENT,
`name`VARCHAR(20) DEFAULT NULL,
`deptId`INT(11)DEFAULT NULL,
PRIMARY KEY (`id`),
KEY`idx_dept_id`(`deptId`)
)ENGINE=INNODB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

INSERT INTO tbl_dept(deptName,locAdd)VALUES('RD',11);
INSERT INTO tbl_dept(deptName,locAdd)VALUES('HR',12);
INSERT INTO tbl_dept(deptName,locAdd)VALUES('MK',13);
INSERT INTO tbl_dept(deptName,locAdd)VALUES('MIS',14);
INSERT INTO tbl_dept(deptName,locAdd)VALUES('FD',15);

INSERT INTO tbl_emp(NAME,deptId)VALUES('z3',1);
INSERT INTO tbl_emp(NAME,deptId)VALUES('z4',1);
INSERT INTO tbl_emp(NAME,deptId)VALUES('z5',1);
INSERT INTO tbl_emp(NAME,deptId)VALUES('w5',2);
INSERT INTO tbl_emp(NAME,deptId)VALUES('w6',2);
INSERT INTO tbl_emp(NAME,deptId)VALUES('s7',3);
INSERT INTO tbl_emp(NAME,deptId)VALUES('s8',4);
INSERT INTO tbl_emp(NAME,deptId)VALUES('s9',51);

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2、以上面的建表为例，测试七种JOIN

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1、select * from tbl_emp a inner join tbl_dept b on a.deptId =b.id;

2、select * from tbl_emp a left join tbl_dept b on a.deptId =b.id;

3、select * from tbl_emp a right join tbl_dept b on a.deptId =b.id;

4、select * from tbl_emp a left join tbl_dept b on a.deptId =b.id where b.id is null;
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5、select * from tbl_emp a right join tbl_dept b on a.deptId =b.id where a.deptId is null;
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6、MySQL不支持full outer join 这样的语法，但是在oracle可以适用。
select * from tbl_emp a full outer join tbl_dept b on a.deptId =b.id;
此时我们可以使用union去重操作将两张表的左连接和右连接相加

select * from tbl_emp a left join tbl_dept b on a.deptId =b.id  
union 
select * from tbl_emp a right join tbl_dept b on a.deptId =b.id;

a，b表的公有+a表的独有+b表的独有 在这里插入图片描述

7、查询a,b表各自的独有

select * from tbl_emp a left join tbl_dept b on a.deptId =b.id  where b.id is null
union 
select * from tbl_emp a right join tbl_dept b on a.deptId =b.id where a.deptId is null;

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