一、基本查询
select
length('abc') "长度",
length('abc') as "长度",
length('abc') as 长度,
length('abc') as '123' from dual;
select distinct job from emp;
select concat('a' , 'b') from dual;
select concat(concat('a' , 'b'),'c') from dual;
select 'a' || 'b'|| 'c' from dual;
select '1' + 1 from dual;
select sal * 12 + nvl(comm,0),nvl(comm,0) from emp;
二、条件查询
select * from emp where comm > 0;
select * from emp where comm is not null and comm != 0;
select * from emp where comm is null or comm = 0;
select * from emp where not(comm is not null and comm != 0);
select * from emp where to_char(hiredate,'yyyy') = '1981';
select * from emp where hiredate >= to_date('1981-01-01','yyyy-mm-dd')
and hiredate <= to_date('1981-12-31','yyyy-mm-dd');
select * from emp where hiredate between to_date('1981-01-01','yyyy-mm-dd')
and to_date('1981-12-31','yyyy-mm-dd') ;
select sysdate,to_char(sysdate,'yyyy-mm-dd hh24:mi:ss day') from dual;
select '2018-07-06 11:11:11' ,
to_date('2018-07-06 11:11:11' ,'yyyy-mm-dd hh24:mi:ss') from dual;
select * from emp where upper(ename) like upper('%M%');
select * from emp order by sal asc;
select * from emp order by sal desc;
select * from emp order by nvl(comm,0) asc;
select * from emp order by comm asc nulls first;
select * from emp order by comm desc nulls last;
三、单行函数
select length(ename) from emp;
select substr('abcjavadef' , 4, 4 ) from dual;
select substr('abcjavadef' , 1, 3 ) from dual;
select substr('abcjavadef' , 0, 3 ) from dual;
select replace('abcdefa' , 'a' ,'z') from dual;
select trim(' abc '),ltrim(' abc '),rtrim(' abc ') from dual;
select sysdate - hiredate from emp;
select (sysdate - hiredate) / 7 from emp;
select months_between(sysdate , hiredate) from emp;
select add_months(sysdate ,-12) from dual;
select round(2.666) from dual;
select trunc(2.666,1) from dual;
select mod(3,10) from dual;
select 1 ,to_char(1),'1',to_number('1') from dual;
select 1 + '1' from dual;
四、多行函数
select
count(1),deptno, avg(sal),max(sal) ,min(sal) ,sum(sal)
from emp group by deptno;
select count(1),deptno from emp group by deptno having count(1) > 4;