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Linux常见指令

alanwhy 2023-06-16 阅读 30

联接

七种JOIN介绍

图形联接方式说明SQL
在这里插入图片描述内联接共有部分SELECT <select_list> FROM TableA A INNER JOIN TableB B ON A.Key = B.Key;
[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-mQHmQOL5-1686824977738)(assets/1686824851787-1.png)]左联接A表独有+共有部分SELECT <select_list> FROM TableA A LEFT JOIN TableB B ON A.Key = B.Key;
在这里插入图片描述右联接B表独有+共有部分SELECT <select_list> FROM TableA A RIGHT JOIN TableB B ON A.Key = B.Key;
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在这里插入图片描述B的独有SELECT <select_list> FROM TableA A RIGHT JOIN TableB B ON A.Key = B.Key WHERE A.Key IS NULL;
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[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-w50kiG6r-1686824977739)(assets/1686824851787-6.png)]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);

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笛卡尔积

select * from tbl_emp,tbl_dept;

5条数据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"

内联接

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

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左联接

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

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右联接

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

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A表独有

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

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B表独有

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

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全联接

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尝试换一种方式实现:A的独有+共有+B的独有

实现方式一:左联接+右联接+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;

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实现方式二:左联接+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

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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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