连接

七种JOIN介绍

图形	连接方式	说明	SQL
	内连接	共有部分	SELECT <select_list> FROM TableA A INNER JOIN TableB B ON A.Key = B.Key;
	左连接	A表独有+共有部分	SELECT <select_list> FROM TableA A LEFT JOIN TableB B ON A.Key = B.Key;
	右连接	B表独有+共有部分	SELECT <select_list> FROM TableA A RIGHT JOIN TableB B ON A.Key = B.Key;
		A的独有	SELECT <select_list> FROM TableA A LEFT JOIN TableB B ON A.Key = B.Key WHERE B.Key IS NULL;
		B的独有	SELECT <select_list> FROM TableA A RIGHT JOIN TableB B ON A.Key = B.Key WHERE A.Key IS NULL;
	全连接	A的独有+共有部分+B的独有	SELECT <select_list> FROM TableA A FULL OUTER JOIN TableB B ON A.Key = B.Key; MySQL不支持FULL OUTER JOIN这种语法
		A独有+B独有	SELECT <select_list> FROM TableA A FULL OUTER JOIN TableB B ON A.Key = B.Key WHERE A.Key IS NULL OR B.Key IS NULL; MySQL不支持FULL OUTER JOIN这种语法

练习

建表+存储数据

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 `fk_dept_id`(`deptId`)
)ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8;

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 CHARACTER SET = 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);

笛卡尔积

select * from tbl_emp,tbl_dept;

5条数据和8条数据两两组合，一共40条，结果如下

"id"       "name"     "deptId"    "id"      "deptName"   "locAdd"
"1"        "z3"        "1"        "5"        "FD"        "15"
"1"        "z3"        "1"        "4"        "MIS"        "14"
"1"        "z3"        "1"        "3"        "MK"        "13"
"1"        "z3"        "1"        "2"        "HR"        "12"
"1"        "z3"        "1"        "1"        "RD"        "11"
"2"        "z4"        "1"        "5"        "FD"        "15"
"2"        "z4"        "1"        "4"        "MIS"        "14"
"2"        "z4"        "1"        "3"        "MK"        "13"
"2"        "z4"        "1"        "2"        "HR"        "12"
"2"        "z4"        "1"        "1"        "RD"        "11"
"3"        "z5"        "1"        "5"        "FD"        "15"
"3"        "z5"        "1"        "4"        "MIS"        "14"
"3"        "z5"        "1"        "3"        "MK"        "13"
"3"        "z5"        "1"        "2"        "HR"        "12"
"3"        "z5"        "1"        "1"        "RD"        "11"
"4"        "w5"        "2"        "5"        "FD"        "15"
"4"        "w5"        "2"        "4"        "MIS"        "14"
"4"        "w5"        "2"        "3"        "MK"        "13"
"4"        "w5"        "2"        "2"        "HR"        "12"
"4"        "w5"        "2"        "1"        "RD"        "11"
"5"        "w6"        "2"        "5"        "FD"        "15"
"5"        "w6"        "2"        "4"        "MIS"        "14"
"5"        "w6"        "2"        "3"        "MK"        "13"
"5"        "w6"        "2"        "2"        "HR"        "12"
"5"        "w6"        "2"        "1"        "RD"        "11"
"6"        "s7"        "3"        "5"        "FD"        "15"
"6"        "s7"        "3"        "4"        "MIS"        "14"
"6"        "s7"        "3"        "3"        "MK"        "13"
"6"        "s7"        "3"        "2"        "HR"        "12"
"6"        "s7"        "3"        "1"        "RD"        "11"
"7"        "s8"        "4"        "5"        "FD"        "15"
"7"        "s8"        "4"        "4"        "MIS"        "14"
"7"        "s8"        "4"        "3"        "MK"        "13"
"7"        "s8"        "4"        "2"        "HR"        "12"
"7"        "s8"        "4"        "1"        "RD"        "11"
"8"        "s9"        "51"        "5"        "FD"        "15"
"8"        "s9"        "51"        "4"        "MIS"        "14"
"8"        "s9"        "51"        "3"        "MK"        "13"
"8"        "s9"        "51"        "2"        "HR"        "12"
"8"        "s9"        "51"        "1"        "RD"        "11"

内连接

SELECT * FROM tbl_emp a INNER JOIN tbl_dept b ON a.deptId = b.id;

左连接

SELECT * FROM tbl_emp a LEFT JOIN tbl_dept b ON a.deptId = b.id;

右连接

SELECT * FROM tbl_emp a RIGHT JOIN tbl_dept b ON a.deptId = b.id;

A表独有

SELECT * FROM tbl_emp a LEFT JOIN tbl_dept b ON a.deptId = b.id WHERE b.id is null;

B表独有

SELECT * FROM tbl_emp a RIGHT JOIN tbl_dept b ON a.deptId = b.id WHERE a.deptId is null;

全连接

尝试换一种方式实现：A的独有+共有+B的独有

实现方式一：左连接+右连接+公共部分去重

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;

实现方式二：左连接+B独有

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 WHERE a.deptId is null;

A独有+B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;