Mysql Join- join query (in)

Mysql Join- join query (in)

understanding

I usually just the data of the contact point of view, there is no connection query is complex enough to be a great need for patience and logic, check out the little point data, stitching, etc. no skills, the more practice will be. Nothing more than between tables according to the common key connection, with union query, where, sub-query these ... really is not difficult, is irritated, sometimes nested many layers, will faint.

achieve

Here the Internet to find some training exercises query data do demonstrate, in fact, training materials market face, how to say, the advantage of wide coverage, emphasis on applications, the disadvantage is very shallow, only suitable for beginners to understand .

• Department table dept (id, name)
• 员工表emp(id, name, gender, salary, join_date, dept_id)
• The associated key: dept.id ~ dept_id (I do not have a foreign key)

Prepare data

-- mysql -u root -p ....
-- show database;
-- use cj;
-- show tables;
-- 新建表格测试数据
drop table if exists emp;
drop table if exists dept;

create table dept(
    id int primary key auto_increment,
    name varcahr(20)
);
-- 员工表
create table emp(
    id int primary key auto_increment,
    name varchar(20),
    gender char(1),
    salary double,
    join_date date,
    dept_id int
);

-- 插入测试数据
insert into dept(name) values
("市场部"), ("财务部"), ("研发部");

insert into emp values
(0, '老三','男',20000,'2016-02-24',1);
(0, '老二','男',18000,'2017-12-02',2);
(0, '亚洲','男',17000,'2018-08-08',1);
(0, '油油','女',14000,'2018-10-07',3);
(0, '老四','女',15000,'2014-03-14',1);
(0, '阳哥','男',3000,'2019-03-14',null);

-- 查看
select * from emp;
+----+------+--------+--------+------------+---------+
| id | name | gender | salary | join_date  | dept_id |
+----+------+--------+--------+------------+---------+
|  1 | 老三 | 男     |  20000 | 2016-02-24 |       1 |
|  2 | 老二 | 男     |  18000 | 2017-12-02 |       2 |
|  3 | 亚洲 | 男     |  17000 | 2018-08-08 |       1 |
|  4 | 油油 | 女     |  14000 | 2018-10-07 |       3 |
|  5 | 老四 | 女     |  15000 | 2014-03-14 |       1 |
|  6 | 阳哥 | 男     |   3000 | 2019-03-14 | NULL    |
+----+------+--------+--------+------------+---------+

select * from dept;
+----+--------+
| id | name   |
+----+--------+
|  1 | 市场部 |
|  2 | 财务部 |
|  3 | 研发部 |

Small scale join and subquery

Scalar query

-- 查询工资最高的员工信息
-- 子查询(标量): 先查出高的工资, 然后作为where的条件
select * 
from emp e
where
    e.salary = (
        select max(salary)
        from emp
    );
  
 +----+------+--------+--------+------------+---------+
| id | name | gender | salary | join_date  | dept_id |
+----+------+--------+--------+------------+---------+
|  1 | 老三 | 男     |  20000 | 2016-02-24 |       1 |
+----+------+--------+--------+------------+---------+

Liezi inquiry, with the judge in

-- 查询 市场部 和 研发部 的信息

-- where (emp.dept_id) IN (dept.id 中符合条件的IDS)
select * 
from emp e
where e.dept_id in (
    select id
    from dept d
    where d.name in ("市场部", "研发部")
);

+----+------+--------+--------+------------+---------+
| id | name | gender | salary | join_date  | dept_id |
+----+------+--------+--------+------------+---------+
|  1 | 老三 | 男     |  20000 | 2016-02-24 |       1 |
|  3 | 亚洲 | 男     |  17000 | 2018-08-08 |       1 |
|  4 | 油油 | 女     |  14000 | 2018-10-07 |       3 |
|  5 | 老四 | 女     |  15000 | 2014-03-14 |       1 |
+----+------+--------+--------+------------+---------+

-- 方案2 表连接inner join 再进行过滤
select *
from (
    select e.*, d.name as "部门"
    from emp e, dept d
    where e.dept_id = d.id 
 ) as a
where a.部门 in ("市场部", "研发部");
    
-- 方案3 改进2
select e.*, d.name as "部门"
from emp e, dept d
where (
    (e.dept_id = d.id) and
    (d.name in ("市场部", "财务部"))
);

Query specific fields, respectively, with sub-queries and join to achieve

-- 查询2018年后入职的员工id, 姓名, 日期, 部门名称

-- 技巧: 先连接表 as别名, 通过别名where... , 最后再写查询字段
select * 
from 
    emp as e
    dept d -- as 可省略
where 
    e.xxx 
    d.xxx 
    
-- 最后再写要查询的字段
select e.xx, e.xx, d.xx

select e.id, e.name, e.join_date, d.name as "部门"
from 
    emp e,
    dept d
where 
    e.dept_id = d.id  -- 没有部门的不算哦
    and e.join_date >= "2018/1/1";
    
+----+------+------------+--------+
| id | name | join_date  | 部门   |
+----+------+------------+--------+
|  3 | 亚洲 | 2018-08-08 | 市场部 |
|  4 | 油油 | 2018-10-07 | 研发部 |
+----+------+------------+--------+

-- 方案2 子查询
select e.id, e.name, e.join_date, d.name
from (
    -- 先提前筛选出来
    select * 
    from emp
    where join_date >="2018/1/1"
) as e,
dept as d
where e.dept_id = d.id;

Exercises to strengthen the join

Prepare data

• Department table dept (id, d_ame, location)
• Post table job (id, j_name, description)
• 员工表 emp(id, e_name, job_id, leader, join_date, salary, bonus, dept_id)
• Wage scales salary_grade (grade, s_min, s_max)
• Relevance (do not adhere to the foreign key) job.id ~ emp.job_id, emp.dept_id ~ dept.id

drop table if exists dept;
drop table if exists job;
drop table if exists emp;
drop table if exists salary_grade;

-- 部门表
create table dept(
    id int primary key,
    d_name varchar(20),
    location varchar(30)
);

-- 岗位表
create table job(
    id int primary key,
    j_name varchar(20),
    description varchar(30)  
);

-- 员工表
create table emp(
    id int primary key,
    e_name varchar(10),
    job_id int,
    leader varchar(10), -- 直属领导
    join_date date,
    salary decimal(8,2),
    bonus decimal(7,2), -- 奖金
    dept_id int
);

-- 工资等级表
create table salary_grade(
    grade int primary key, -- 级别
    s_min int, -- 下界
    s_max int -- 上界
);

-- 添加测试数据 
INSERT INTO dept VALUES 
(10,'研发部','深圳'),
(20,'产品部','深圳'),
(30,'销售部','广州'),
(40,'财务部','上海');

 INSERT INTO job (id, j_name, description) VALUES
 (1, 'CEO', '管理整个公司，接单'),
 (2, '经理', '管理部门员工'),
 (3, '销售', '向客户销售商品'),
 (4, '文员', '职能管理');
 
 
 insert into salary_grade values 
 (1,7000,12000),
 (2,12010,14000),
 (3,14010,20000),
 (4,20010,30000),
 (5,30010,99990);


INSERT INTO emp VALUES 
(1001,'孙悟空',4,1004,'2014-12-17','8000.00',NULL,20),
(1002,'卢俊义',3,1006,'2001-02-20','16000.00','3000.00',30),
(1003,'林冲',3,1006,'2001-02-22','12500.00','5000.00',30),
(1004,'唐僧',2,1009,'2018-04-02','29750.00',NULL,20),
(1005,'李逵',4,1006,'2017-09-28','12500.00','14000.00',30),
(1006,'宋江',2,1009,'2015-05-01','28500.00',NULL,30),
(1007,'刘备',2,1009,'2019-09-01','24500.00',NULL,10),
(1008,'猪八戒',4,1004,'2007-04-19','30000.00',NULL,20),
(1009,'罗贯中',1,NULL,'2016-11-17','50000.00',NULL,10),
(1010,'吴用',3,1006,'2017-09-08','15000.00','0.00',30),
(1011,'沙僧',4,1004,'2012-05-23','11000.00',NULL,20),
(1012,'李逵',4,1006,'2008-12-03','9500.00',NULL,30),
(1013,'小白龙',4,1004,'2016-12-03','30000.00',NULL,20),
(1014,'关羽',4,1007,'2019-01-23','13000.00',NULL,10);

Preview wave test data

-- 预览一波
mysql> select * from dept;
+----+--------+----------+
| id | d_name | location |
+----+--------+----------+
| 10 | 研发部 | 深圳     |
| 20 | 产品部 | 深圳     |
| 30 | 销售部 | 广州     |
| 40 | 财务部 | 上海     |
+----+--------+----------+

mysql> select * from job;
+----+--------+--------------------+
| id | j_name | description        |
+----+--------+--------------------+
|  1 | CEO    | 管理整个公司，接单 |
|  2 | 经理   | 管理部门员工       |
|  3 | 销售   | 向客户销售商品     |
|  4 | 文员   | 职能管理           |
+----+--------+--------------------+

mysql> select * from salary_grade;
+-------+-------+-------+
| grade | s_min | s_max |
+-------+-------+-------+
|     1 |  7000 | 12000 |
|     2 | 12010 | 14000 |
|     3 | 14010 | 20000 |
|     4 | 20010 | 30000 |
|     5 | 30010 | 99990 |
+-------+-------+-------+

mysql> select * from emp limit 5;
+------+--------+--------+--------+------------+----------+----------+---------+
| id   | e_name | job_id | leader | join_date  | salary   | bonus    | dept_id |
+------+--------+--------+--------+------------+----------+----------+---------+
| 1001 | 孙悟空 |      4 | 1004   | 2014-12-17 | 8000.00  | NULL     |      20 |
| 1002 | 卢俊义 |      3 | 1006   | 2001-02-20 | 16000.00 | 3000.00  |      30 |
| 1003 | 林冲   |      3 | 1006   | 2001-02-22 | 12500.00 | 5000.00  |      30 |
| 1004 | 唐僧   |      2 | 1009   | 2018-04-02 | 29750.00 | NULL     |      20 |
| 1005 | 李逵   |      4 | 1006   | 2017-09-28 | 12500.00 | 14000.00 |      30 |
+------+--------+--------+--------+------------+----------+----------+---------+

Case1: ( 2 tables ) query employee information, including employee number, name, salary, job title, job description

• Process: combed table and related fields; connection condition table
• Tips: from> WHERE> Group and by aggregation function> having> order> select

analysis:

• emp表: id, e_name, salary
• job表: j_name, description
• Join conditions: left join the connector or, emp.job_id = jop.id

-- 用left join, 平时excel 的vlookup 就是这样玩的
select *
from emp e
    left join job d
    on e.job_id = d.id;

select 
    e.id,
    e.e_name,
    e.salary,
    d.j_name,
    d.description
from emp e
    left join job d
    on e.job_id = d.id;

-- out
+------+--------+----------+--------+--------------------+
| id   | e_name | salary   | j_name | description        |
+------+--------+----------+--------+--------------------+
| 1009 | 罗贯中 | 50000.00 | CEO    | 管理整个公司，接单 |
| 1004 | 唐僧   | 29750.00 | 经理   | 管理部门员工       |
| 1006 | 宋江   | 28500.00 | 经理   | 管理部门员工       |
| 1007 | 刘备   | 24500.00 | 经理   | 管理部门员工       |
| 1002 | 卢俊义 | 16000.00 | 销售   | 向客户销售商品     |
| 1003 | 林冲   | 12500.00 | 销售   | 向客户销售商品     |
| 1010 | 吴用   | 15000.00 | 销售   | 向客户销售商品     |
| 1001 | 孙悟空 | 8000.00  | 文员   | 职能管理           |
| 1005 | 李逵   | 12500.00 | 文员   | 职能管理           |
| 1008 | 猪八戒 | 30000.00 | 文员   | 职能管理           |
| 1011 | 沙僧   | 11000.00 | 文员   | 职能管理           |
| 1012 | 李逵   | 9500.00  | 文员   | 职能管理           |
| 1013 | 小白龙 | 30000.00 | 文员   | 职能管理           |
| 1014 | 关羽   | 13000.00 | 文员   | 职能管理           |
+------+--------+----------+--------+--------------------+

Case2: ( 3 tables ) query employee number, name, salary, job title, department name, department, location

• emp表: id, e_name, salary
• job表: j_name
• dept表: d_name, location
• Connection: left connected, emp.job_id = job.id, emp.dept_id = dept.id

-- 我通常是先全部查出来, 再进行where
select * 
from emp e
    left join job j
    on e.job_id = j.id
    left join dept d  -- 继续连
    on e.dept_id = d.id;

select
    e.id,
    e.e_name,
    e.salary,
    j.j_name,
    -- d.d_name,
    d.location
from emp e
    left join job j
    on e.job_id = j.id
    -- 继续连接...
    left join dept d
    on e.dept_id = d.id
limit 3;

+------+--------+----------+--------+----------+
| id   | e_name | salary   | j_name | location |
+------+--------+----------+--------+----------+
| 1009 | 罗贯中 | 50000.00 | CEO    | 深圳     |
| 1004 | 唐僧   | 29750.00 | 经理   | 深圳     |
| 1006 | 宋江   | 28500.00 | 经理   | 广州     |
+------+--------+----------+--------+----------+

case3: query employee name, salary, wage levels (between .... and, judging conditions do the Join )

analysis

• emp表: e_name, salary
• salary_grade表: grade
• Connecting conditions: JOIN, e.salary BETWEEN s.s_min AND s.s_max

select 
    e.e_name,
    e.salary as "薪资",
    s.grade as "薪资等级"
from emp e
    join
    salary_grade s
    on e.salary between s.s_min and s.s_max
limit 5;
    
+--------+----------+----------+
| e_name | 薪资     | 薪资等级 |
+--------+----------+----------+
| 孙悟空 | 8000.00  |        1 |
| 卢俊义 | 16000.00 |        3 |
| 林冲   | 12500.00 |        2 |
| 唐僧   | 29750.00 |        4 |
| 李逵   | 12500.00 |        2 |
+--------+----------+----------+
5 rows in set (0.11 sec)

Case 4: ( 4 tables ) query employee name, salary, position, department, department location, pay grade

analysis

• emp表: e_name, salary
• job表: j_name
• dept表: d_name, location
• salary_grade表: grade
• Connection condition e, j, d, s:
  • e.job_id = j.id
  • e.dept_id = d.id
  • e.salary BETWEEN s.s_min AND s.s_max

select *
from emp e             
    left join job j    -- 职位表
    ON e.job_id = j.id
    left join dept d   -- 部门表
    ON e.dept_id = d.id
    join salary_grade s -- 薪资等级表
    ON e.salary between s.s_min and s.s_max
    
limit 1;
    

He left stitching a piece of super large table

+------+--------+--------+--------+------------+----------+---------+---------+----+--------+----------------+----+--------+----------+-------+-------+-------+
| id   | e_name | job_id | leader | join_date  | salary   | bonus   | dept_id | id | j_name | description    | id | d_name | location | grade | s_min | s_max |
+------+--------+--------+--------+------------+----------+---------+---------+----+--------+----------------+----+--------+----------+-------+-------+-------+
| 1001 | 孙悟空 |      4 | 1004   | 2014-12-17 | 8000.00  | NULL    |      20 |  4 | 文员   | 职能管理       | 20 | 产品部 | 深圳     |     1 |  7000 | 12000 |

select 
    e.e_name, 
    e.salary,
    j.j_name,
    d.d_name,
    d.location,
    s.grade
from emp e             
    left join job j    -- 职位表
    ON e.job_id = j.id
    left join dept d   -- 部门表
    ON e.dept_id = d.id
    join salary_grade s -- 薪资等级表
    ON e.salary between s.s_min and s.s_max
    
limit 5;
    
+--------+----------+--------+--------+----------+-------+
| e_name | salary   | j_name | d_name | location | grade |
+--------+----------+--------+--------+----------+-------+
| 孙悟空 | 8000.00  | 文员   | 产品部 | 深圳     |     1 |
| 卢俊义 | 16000.00 | 销售   | 销售部 | 广州     |     3 |
| 林冲   | 12500.00 | 销售   | 销售部 | 广州     |     2 |
| 唐僧   | 29750.00 | 经理   | 产品部 | 深圳     |     4 |
| 李逵   | 12500.00 | 文员   | 销售部 | 广州     |     2 |
+--------+----------+--------+--------+----------+-------+

case5: Query department number, name, location, number of people, the Join another group by, an aggregate function, etc.

Analysis: connect, and then press department packet aggregation to +

• dept表: id, d_name, location
• emp table: id (used to count)
• Join conditions: do connect dept.id = emp.dept_id

select 
    d.id,
    d.d_name,
    d.location,
    -- 不要count(*) null 不加入计算哦
    count(e.id) as "人数"
from dept d
    left join emp e
    on d.id = e.dept_id
-- 按部门分组
group by d.d_name;

+----+--------+----------+------+
| id | d_name | location | 人数 |
+----+--------+----------+------+
| 20 | 产品部 | 深圳     |    5 |
| 10 | 研发部 | 深圳     |    3 |
| 40 | 财务部 | 上海     |    0 |
| 30 | 销售部 | 广州     |    6 |
+----+--------+----------+------+

case6: ( self-join ) query the employee's name, its leadership

Analysis: as self-aliasing by connecting (id field and field leader autocorrelation oh)

• emp table e1: e_name
• emp table e2: e.leader
• Connection conditions: left connecting, e1.leader = e2.id

select 
    e1.e_name as "员工姓名",
    e1.e_name as "直属领导"
from emp as e1
    left join emp as e2
    on e1.leader = e2.id;
    
limit 5;
    
+----------+----------+
| 员工姓名 | 直属领导 |
+----------+----------+
| 孙悟空   | 孙悟空   |
| 卢俊义   | 卢俊义   |
| 林冲     | 林冲     |
| 唐僧     | 唐僧     |
| 李逵     | 李逵     |
+----------+----------+
14 rows in set (0.11 sec)

to sum up

• Table connection I use frequency left join> inner join
• Connection field on equivalent conditions can be determined, or
• The key is that the multi-table joins which table and field analysis required to determine the connection mode, whether or polymeric nested ...
• Technically, try to write sql statement standardization easy to read, from> the WHERE> Group by and aggregate functions> having> order> select
• Strengthen again next wave of self-ligation (linkage provinces, municipalities or fans interact) and combined union, group by + aggregation of these it ...