DML:Data Manipulation Language 数据操作语言
包括：CRUD
1. insert语句
(1) 从其它表中复制数据,实现方法:在insert 语句中加入查询语句
insert into sales_reps(id,name,salary,commission_pct) select employee_id,last_name,salary,commission_pct
from employees where job_id like '%rep';
(2) update中使用子查询
update employees set job_id = (select job_id from employees where employee_id = 205),
salary = (select salary from employees where employee_id = 205)
where employee_id = 114;
如：更新114号员工的工作和工资使其与205号员工相同
update employees set job_id = (select job_id from employees where employee_id = 205),
salary = (select salary from employees where employee_id = 205)
where employee_id = 114
再看一个问题，仔细体会解决步骤：
更改 108 员工的信息: 使其 工资变为所在部门中的最高工资，job变为公司中平均工资最低的job
分析：
第1 步 首先查询 108 所在部门的最高工资是多少
select max(salary) from employees where department_id =
( select department_id from employees where employee_id = 108)
第 2 步 查询公司中平均工资最低的 job_id
select job_id from employees group by job_id having avg(salary) =
(select min(avg_sal) from(select avg(salary) avg_sal from employees group by job_id) )
第 3 步 实现更新
update employees set salary = ( select max(salary) from employees
where department_id = (select department_id from employees where employee_id = 108),
job_id = ( select job_id from employees group by job_id
having avg(salary) =(select min(avg_sal) from(select avg(salary)avg_sql from employees
group by job_id ) ) )
where job_id = 108
(3)在delete 中使用子查询
eg: 删除 108 号员工所在部门的工资最低的员工
delete from employees where salary =(select min(salary) from employees where
department_id = (select department_id from employees where employee_id = 108 ) )