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PLSQL????????

?PLSQL??????????????????????????to_date?to_char?????????????????????????????PLSQL????????????????decode???NVL???????????????

??????????????????????PLSQL??????????????????

select to_date('2005-01-01 13:14:20','yyyy-MM-dd HH24:mi:ss') from dual;

????????'2005-01-01 13:14:20'??'yyyy-MM-dd HH24:mi:ss'????????????????????????

?????????????????????????????

select to_date('2005-01-01 13:14:20','yyyy-MM-dd') from dual;

???????PLSQL?to_date?????????????????????????????????????????????????

??????????????????????????????????????

select to_char(sysdate,'yyyy-MM-dd HH24:mm:ss') from dual;

?????????????????????????????????????????????

select to_char(sysdate,'yyyy-MM-dd') from dual;

????????????????????????????null?????????????decode????????????

decode('2005-01-01','yyyy-MM-dd', '????', '????') as result

??????null?????????????????

decode('????', 'yyyy-MM-dd', '????', default) as result

????????????????NVL??????????????

select nvl(comm, 0) as salary from emp

NVL?????comm???????????0????????????

???????????????????NVL2???NVL2?????????????????????????

select nvl2(comm, sal + comm, sal) as salary from emp

?????????????????????????????????

select nvl2(comm, sal + comm, sal, sal) from emp

???????NVL2???Oracle 9i?????????

???????????PLSQL???????????????????????????PLSQL?????????????