Oracle base SQL语句

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----------常用函数  -------------
--nvl函数  如果 exp1 为空，则返回 exp2
Select nvl(comm,0) From emp
--nullif函数  如果 exp1 和 exp2 相等，则返回 null ，否则返回 exp1
Select nullif(1,2) From dual
--nvl2函数  如果 exp1 不为空，则返回 exp2 ，否则返回 exp3
Select empno,ename,sal,comm,nvl2(comm,sal+comm,sal) total From emp
--coalesce函数  遇到非空即返回
Select empno,ename,sal,comm,coalesce(sal+comm,sal,0) total From emp
--case函数
Select empno,ename,sal,
Case deptno
When 10 Then '财务部'
When 20 Then '研发部'
When 30 Then '销售部'
Else '未知部门'
End 部门
From emp;
--decode函数
Select empno,ename,sal,
decode(deptno,10,'财务部',
20,'研发部',
30,'销售部',
'未知部门'
) 部门
From emp;

--多行子查询，子查询返回不是一个结果的
Select * From emp Where sal>Any(Select Avg(sal) From emp Group By deptno);
Select * From emp Where sal>All(Select Avg(sal) From emp Group By deptno);
Select * From emp Where job In (Select job From emp Where ename='MARTIN' Or ename='SMTTH')
--分页查询第一种写法
select * from (
select rownum no,e.* from (
select * from emp order by sal Desc
) e where rownum<=5
) where no>=3;
--分页查询第二种写法
select * from (
select rownum no,e.* from (
select * from emp order by sal Desc
) e
) where no>=3 and no<=5;
--随机返回五行数据
Select * From (
Select empno,ename,job From emp Order By dbms_random.value()      
) Where Rownum <= 5;
Select * From emp Order By sal

--首字母转为大写
Select initcap(ename) From emp
--连接字符串
Select concat('hello ','word') From dual
--截取字符串
Select substr(ename,-3,3) From emp
--四舍五入
Select round(789.567,-2) From dual
--直接取几位，不四舍五入
Select trunc(789.576,-2) From dual
--雇佣了几周
Select round((Sysdate-hiredate)/7) From emp
--年 月 日
Select empno,ename,to_char(hiredate,'yyyy') Year,to_char(hiredate,'mm') months,to_char(hiredate,'dd') Day From emp
--格式化为制定时间格式
Select empno,ename,to_char(hiredate,'yyyy-mm-dd') From emp
--去零
Select empno,ename,to_char(hiredate,'fmyyyy-mm-dd') From emp
--美元
Select empno,ename,to_char(sal,'$99,999') From emp
--本地
Select empno,ename,to_char(sal,'L99,999') From emp
--年薪资 （工资+奖金）×12
Select empno,ename,nvl(comm,0),(sal+nvl(comm,0))*12 income From emp
--奖金不为空
Select Distinct job From emp Where comm Is Not Null
--每月倒数第三天雇佣的员工信息
Select * From emp Where Last_day(hiredate)-2=hiredate
--最高12年前雇佣的，今天和雇佣日期之间总月份/12
Select * From emp Where months_between(Sysdate,hiredate)/12 > 12
--雇佣了多少天
Select ename,round(Sysdate-hiredate) From emp
Select * From emp
--工作年限，月限
Select ename,trunc(months_between(Sysdate,hiredate)/12) Year,
trunc(Mod(months_between(Sysdate,hiredate),12)) months
From emp