????26.?????????????“A”?????????н???1000???????????1000????????????????
?????????? ??????
????select * from emp where ename like ‘%A%’ and sal > 1000;
????27.???????????????????“M”??????????????
??????????????????? __M%
????select * from emp where ename like ‘__M%';
????28.???????????н?????????н??????????????併??????
??????????select * from emp order by sal asc??hiredate desc;
????29.???????????????????????????????????????????н?????????
??????????SUBSTRING(‘?????’????????????????);  —- ????? substring(ename??1??1)
????select * from emp order by substring(ename??1??1) asc??sal desc;
????30.??????繤??????????????????????н???
???????????繤???? — hiredate С?
????select ename??hiredate??sal from emp where hiredate = (select min(hiredate) from emp);
????select ename??hiredate??sal from emp where hiredate <= all(select hiredate from emp);
????> any === > min
????> all === > max
????< any === < max
????< all === < min
????31.?????????????????н????????????н?????????100.
??????????select ename??sal??comm from emp; —- ??н??????100  ????ifnull
????select ename??sal??ifnull(comm??100) from emp;
????32.?????н???????λ??
????????: select job from emp where sal = (select max(sal) from emp);
????select job from emp where sal >= all(select sal from emp);
????33.???emp???????в?????н????н??????????10???????????
??????????????????? select deptno??max(sal)??min(sal) from emp where deptno<>10 group by deptno;
????34.???10?????н?????????
??????????delete from emp where deptno=10 and sal >= all(select sal from emp where deptno=10 ); // MYSQL ?????
????Mysql ?淶??????????? ???м?????????????????? ????????
????ERROR 1093 (HY000): You can’t specify target table ‘emp’ for update in FROM clause
??????????????????
????delete from emp where deptno=10 and sal >= all(select t.sal from (select sal from emp where deptno=10) t );
????35.??н?????????н???30%??
??????????update emp set sal = sal*0.7 where sal = (select max(sal) from emp); // MYSQL ?????
???????? ?????
????update emp set sal = sal*0.7 where sal = (select t.maxsal  from (select max(sal) maxsal from emp) t);
????36.????????????????? ???????(????>=3000 ?3????????>2000 ?2????????<=2000 ?1??)
??????????
????select ename??sal?? case when sal>=3000 then ‘3??’ when sal>2000 then ‘2??’ else ‘1??’ end ???? from emp;
????????case … when … then … when … then … else … end
???????л???
???????? ?γ? ????
???????? ???? 74
???????? ??? 83
???????? ???? 93
???????? ???? 74
???????? ??? 84
???????? ???? 94
????????(?????????)??
???????? ???? ??? ????
????—- —- —- —-
???????? 74   84   94
???????? 74   83   93
????——————-
????select name??max(case when cource =’????’ then score else 0 end) from scores group by name;
????select name??max(case when cource =’????’ then score else 0 end)  ?????max(case when cource =’???’ then score else 0 end) ?????
????max(case when cource =’???’ then score else 0 end) ???  from scores group by name;