SQL的基本语法练习

select EMPNO,SAL from emp where SAL BETWEEN 1000 and 2000--从enp中获取sal中1000到2000之间的数据
select ENAME,SAL from emp where SAL >= 1000 and SAL <=2000--从enp中获取sal中1000到2000之间的数据
select ENAME,SAL from emp where SAl IN(1000,2300);

select EMPNO from emp ORDER BY EMPNO;--默认排序
select EMPNO from emp ORDER BY EMPNO ASC--升序
select EMPNO from emp ORDER BY EMPNO DESC--降序

select LOWER( ENAME) from emp --大小写的转换

select * from emp;

select * from emp;
select trim(ename) from emp--去掉首尾的空格

select * from emp;
select * from emp where ENAME = ‘KING‘--从中查找某个指定的

select * from emp;
select sal,sal+300 from emp--使用数学运算符“+”
select sal,sal*10 from emp--使用数学运算符“*”
select sal,10*sal+300 from emp--运算符的优先级
select sal,10*(sal+300)from emp--带括好的运算

select * from emp;
select sal+20 AS sal_o from emp

select * from emp;
select ENAME || JOB from emp--连接符的运算
------数值函数-----

round--四舍五入
select round(412,-1) from dual--410
select round(412.777,2) from dual--412.78

trunc--截断
select trunc(412.13,-1) from dual--410

MOD --求余
select MOd(200,11) from emp
select Mod(135.23,15) from dual

--日期函数
Months_between()---两个日期相差的月数
select months_between(sysdate,hiredate) from emp
Last_day---本月的最后一天
select last_day(sysdate) from dual
Next_day()--指定日期的下个日期
select next_day(sysdate,‘星期一‘) from dual
-------------------------------------------------
select * from emp order by sal  DESC
select sal
from emp
order by sal DESC

--------------------------------------------------
Add_months()--向指定日期加上若干月数
select Add_months(sysdate,0) from dual;

-----转换函数----
to_char--对数字的转换
select to_char(sysdate,‘yyyy‘) from dual;
select to_char(sysdate,‘fmyyyy-mm-dd‘) from dual;
select to_char(sal,‘L999,999,999‘) from emp;
select to_char(sysdate,‘D‘) from dual--返回星期

To_number--讲字符转换成数字
select to_number(‘13‘)+to_number(‘14‘) from dual---27

To_date
Select to_date(‘20090210‘,‘yyyyMMdd‘)from dual

------通用函数--
NVL()函数
select nvl(comm,1) from emp

-----------------------------------------------------------------
--模糊查询like
select * from emp
select * from emp
where job like ‘%*_%‘
-----逻辑运算符
--选择在部门30中员工的所有信息
select * from emp
where deptno=30;
--列出职位为（MANAGER）的员工的编号，姓名
select EMPNO,ENAME from emp
where job=‘MANAGER‘
--找出奖金高于工资的员工
select *from emp
where comm>sal
--找出每个员工奖金和工资的总和
select comm+sal,ename from emp
--找出部门10中的经理（MANAGER）和部门20中的普通员工（CLERK）
select * from emp
where (deptno=10 and job=‘MANAGER‘)or(deptno=20 and job=‘CLERK‘)
--找出部门10中既不是经理也不是普通员工，而且工资大于等于2000的员工
select *from emp
where deptno=10 and job not in(‘MANAGER‘,‘CLERK‘) and sal>=2000;
--找出有奖金的员工的不同工作
select distinct job from emp--distinct不同
where comm is not null and comm>0;
--找出没有奖金或奖金低于500的员工
select *from emp
where comm <500 or comm is null;
--显示雇员信息姓名，根据其服务年限，将最老的雇员排在最前面
select ename from emp
order by hiredate;