> / < / >= / <= / != / <> /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...and select * from emp where empno between 7800 and 9000; -- 等同于: select * from emp where empno >= 7800 and empno <= 9000;