1 where 筛选关键字; select * from emp where job 'CLERK' 从emp表中列出 job大于'CLERK'的项 (由于比较的是字符串,所以加单引号) 2 between and select ename,sal from emp where sal between 800 and 1500 从emp表中找到 sal在800和1500之间的项(包括800
1 where 筛选关键字;
select * from emp where job >'CLERK'
从emp表中列出 job值大于'CLERK'的项 (由于比较的是字符串,所以加单引号)
2 between and
select ename,sal from emp where sal between 800 and 1500
从emp表中找到 sal值在800和1500之间的项(包括800和1500) 列出他们的ename 和sal
3 空值
select ename,sal from emp where comm is null ;
列出非空值
select ename,sal from emp where comm is not null ;
4 模糊查询
查询ename中包含ALL的项
select ename from emp where ename like '%ALL%' ;
%代表0个或多个字符, 次查询目的为了找到ename 值为 ALL 左边和右边具有0个或多个字符的项
查询ename第二个字母为A 的项
select ename from emp where ename like '_A%' ;
5 转义字符
查找ename中带有 % 的项
select ename from emp where ename like '%$%%' escape '$' ;
指定'$'为转义字符查找% .
转义字符默认为'/' 使用/ 为转义字符时不用写后面的escape ..
6 排序order by
select * from dept order by deptno ; (默认升序)
select * from dept order by deptno desc ;(按deptno的降序排序)
组合使用:
select empno,ename from emp where empno 10 order by empno; (先过滤 再排序)
select empno,ename from emp order by empno asc,ename desc; 按(empno升序排序) empno相同时按ename 降序排序
