内连接
通过链接把多张表组合成一张临时表
select 表头名 from 表名1 inner join 表名2 ;
select * from employees inner join departments
select 表头名 from 表名1 inner join 表名2 on 链接条件;
select * from employees inner join departments on employees.dept_id = departments.dept_id;
在临时组成新表里，可以在哟以下处理
select 表头名 from 表名1 inner join 表名2 on 链接条件[where | order by | group by| limit | having];
等值链接 ： 前提是链接里有储存相同数据的表头
select * from employees inner join departments on employees.dept_id = departments.dept_id;
定义别名后必须使用别名表示表名
- select e.* , d.dept_name
- from employees as e inner join departments as d on e.dept_id=d.dept_id;
查询每个员工2018年的总工资
select name ,sum(basic+bonus) as total from employees inner join salary on employees.employee_id = salary.employee_id where year(date)=2018 group by name; select salary.employee_id ,sum(basic+bonus) as total from employees inner join salary on employees.employee_id = salary.employee_id where year(date)=2018 group by employee_id having total > 300000 order by total desc ,employee_id asc;查询2018年总工资大于30万的员工，按2018年总工资降序排列
非等值链接： 表里没有存储相同数据的表头
select employee_id ,basic,garde from salary inner join wage_grade on salary.basic between wage_grade.low and wage_grade.high where year(date)=2018 and month(date)=12;
查询2018年12月员工基本工资
select garde as 级别,count(employee_id) as 总人数 from salary inner join wage_grade on salary.basic between wage_grade.low and wage_grade.high where year(date)=2018 and month(date)=12 group by garde;查询2018年12月员工基本工资级别的人数
3张表连接的例子
select name ,basic ,garde from employees inner join salary on employees.employee_id = salary.employee_id inner join wage_grade on salary.basic between wage_grade.low and wage_grade.high where year(date)=2018 and month(date)=12;
外链接查询
外链接是比较2个表的不同
左链接 用左表数据和右表数据作比较 输出结果左表头数据全部显示，
右边仅显示与链接匹配的`行
select 表头名 from 表名1 left jion 表名2 on 链接条件 ;
select 表头名 from 表名1 left jion 表名2 on 链接条件 ·[where |group by| orderby | having | limit] ;
select dept_name, name from departments left join employees on departments.dept_id=employees.dept_id where name is null;
右链接 用右表数据和左表数据作比较 输出结果右表头数据全部显示
右边仅显示与链接匹配的`行
select 表头名 from 表名1 right jion 表名2 on 链接条件 ·[where |group by| orderby | having | limit] ;
mysql> select dept_name,name from departments as d right join employees as e on d.dept_id=e.dept_id where dept_name is null;
update employees set dept_id=11 where name="bob";
全链接查询
把多个select命令查询的行一起数据 多个select查询，表头数要一致
去重行的输出
mysql> (select date , max(basic) as 工资 from salary where date=20180110)union(select date,min(basic) from salary where date=20180110);
（select 查询命令）union （select 查询命令）;
不去重行的输出
select 查询命令）union all（select 查询命令）;
嵌套查询
select 查询命令包含select查询命令
where之后嵌套查询 分组
select 表头名 from 库.表 where 表头名 判断符号 （ select 查询命令）
select employee_id,date,basic,bonus from salary where year(date)=2018 and month(date)=12 and basic > (select basic from salary where year(date)=2018 and month(date)=12 and employee_id=100);
having之后嵌套查询 把（）里的查询结果作为过滤条件，
select 表头名 from 库.表 having 表头名 判断符号 （ select 查询命令）
select dept_id , count(name) as total from employees group by dept_id
having total < (
select count(name) from employees where dept_id=(
select dept_id from departments where dept_name='开发部')
from之后嵌套查询 把（）的查询结果作表使用
select 表头名 from （select 查询结果）as 临时表名 where 筛选条件；
select employee_id ,name,email,dept_name from (select d.dept_name,e.* from departments as d inner join employees as e on d.dept_id=e.dept_id) as tmp_table where dept_id=3;
select之后嵌套查询
select 表头名, (select 查询命令)as 表头名 from 库.表 where 筛选条件;
select d.* ,(select count(name)from employees as e where d.dept_id=e.dept_id)as vumen from departments as d;
