比较运算符

> / < / >= / <= / != / <> /IS NULL / Like / Between / In / Exsist

-- 判断 null 值select * from n5 where s is null;select * from n5 where s is not null;-- like 模糊查询。慎用，有可能会导致全表扫描，效率低。-- % 匹配0到多个字符，_ 匹配一个字符select username from dba_users where username like 'VI_';select username from dba_users where username like 'SC%';select username from dba_users where username like '%SC%';-- in，是 where x = a or x = b or x = c 的一种缩写。下面两条是等价的。select * from emp where empno in (700, 800, 900);select * from emp where empno = 700 or empno = 800 or empno = 900;-- in 后面跟的不一定是逗号分隔的单项，也可能是一个完整的查询语句。-- 下面两条结果是一致的-- 这种 in 慎用select * from emp where deptno in (select deptno from dept where dname = 'SALES');select a.* from emp a,dept d where a.deptno =d.deptno and d.dname='SALES';-- between...andselect * from emp where empno between 7800 and 9000;-- 等同于：select * from emp where empno >= 7800 and empno <= 9000;