Oracle数据库的基本用法

--选取整个表的列
1.   select * from emp;
--选取指定列的内容
select job from emp;
select ename,sal from emp;
--条件判断 
select sal from emp
  where sal=800;
--between and 方法
select * from emp
  where  sal between 2000 and 3000;
--嵌套的使用
select job from 
  (select * from emp
     where  sal between 2000 and 3000);
--单列数据的改变     
select sal+25 from emp;
--用like(模糊)概念  （-一个字符） （% 0个或多个字符）
 select job from emp
   where job like ‘%LE%‘;
--从in（）里面的数据选出   
 select * from emp
   where comm in(300,500);
select sal,sal+25.00 AS saly from emp;
--字符串的连接   AS别名   将job换成ta
select empno,empno+25||‘is a ‘||job AS ta from emp;
--删除重复行 关键词DISTINCT
 select DISTINCT comm from emp;
--用IS NULL 关键字判断为空的情况
 select * from emp
   where comm IS NULL;
 select comm from emp
   where comm IS NULL;