程序员必须知道的数据库增删改查

–insert插入语句

–向员工表中插入数据

insert into emp values(9257,’张三’,’程序远’,007,sysdate,20,null,10);

–创建一个临时表

create table ttemp as select *from emp where 1=2;

–查询结果

insert into ttemp select *from emp;

select *from ttemp;

select *from emp;

–删表

truncate table temp;

–update 更新语句

update emp set mgr=8888,hiredate=sysdate,sal=999,deptno=20 where empno=1245;

–连表查询

–查询员信息，部门名称信息

select *from emp e, dept d where e.deptno =d.deptno;

–查询员工姓名和部门名称

select e.ename,d.dname from emp e,dept d where e.deptno=d.deptno;

–查询员工所有信息和部门名称

select e.*,d.dname from emp e ,dept d where e.deptno=d.deptno;

–查询工资大于3000的员工姓名和工资和部门名称

select e.ename,e.sal,d.dname from emp e ,dept d where e.deptno=d.deptno and e.sal>3000;

–非等值查询

–查询员工的工资等级

select *from emp e,salgrade s where e.sal<=s.hisal and e.sal>s.losal;

–左外连接

select *from emp e,dept d where e.deptno=d.deptno(+);

select *from emp e,dept d where e.deptno(+)=d.deptno;

–自连接

–查询员姓名和员工经理姓名

select e.ename, d.ename from emp e ,emp d where e.mgr=d.empno;

select a.ename,b.ename,c.ename from emp a ,emp b, emp c where a.mgr=b.empno and b.mgr=c.empno;

–cross join 笛卡尔

select *from emp cross join dept d;

–自然连接

select *from emp natural join dept;

–using

select e.ename ,deptno from emp e join dept d using(deptno);

–on 自定义连接条件

select *from emp e join dept d on e.deptno=d.deptno;

select *from emp e join emp e1 on e.mgr=e1.empno;

–查询经理姓名和经理姓名

select e.ename,e1.ename,e2.ename from emp e join emp e1 on e.mgr=e1.empno join emp e2 on e1.mgr= e2.empno;

–inner join两边都合法

select *from emp e inner join dept d on e.deptno=d.deptno;

–left join左连接左表为主

select *from emp e left join dept d on e.deptno=d.deptno;

–right join右边为主

select *from emp e right join dept d on e.deptno=d.deptno;

–full join 全连

select *from emp e full join dept d on e.deptno=d.deptno;

–查询员工姓名和部门姓名和其经理的名字和经理的部门名称

select e.ename, d.dname,e2.ename, d2.dname

from emp e left join dept d on e.deptno=d.deptno left join emp e2

on e.mgr=e2.empno left join dept d2 on e2.deptno=d2.deptno;

–子查询

– 思考：查询工资高于平均工资的雇员名字和工资。

select ename from emp where sal>(select avg(sal) from emp );

– 思考：查询和SCOTT同一部门且比他工资低的雇员名字和工资。

select ename,sal from emp where deptno=(select deptno from emp where ename=’SCOTT’ )and sal<(select sal from emp where ename=’SCOTT’);

– 多行子查询 查询和s,s,c在同一个部门的员工信息并不包含s,s,c;

select * from emp where deptno in(select distinct deptno from emp where ename in(‘SCOTT’,’SMITH’,’CLARK’))and ename not in(‘SCOTT’,’SMITH’,’CLARK’);

–思考：查询工资最高的雇员名字和工资。

select ename,sal from emp where sal=(select max(sal)from emp);

–查询职务和SCOTT相同，比SCOTT雇佣时间早的雇员信息

select *from emp where job=(select job from emp where ename=’SCOTT’)and hiredate<(select hiredate from emp where ename=’SCOTT’);

—- 多行查询

–查询工资低于任何一个“CLERK”的工资的雇员信息。

select *from emp where sal