????????????????<br>RANK()OVER():???????????????????????????????????????????????????????м??????????????<br>DENSE_RANK():??????????????????????????????????????????????????????????????????????????????<br>ROW_NUMBER():????????????????????????????????????????????????????????
????2??TRANSLATE()????

????translate??????replace?????????????replace?????translate????????string?г????from_str????from_str?и???????滻??to_str??λ??????????????to_str?е??????
????SQL Reference?и????????SELECT TRANSLATE('SQL*Plus User''s Guide'?? ' */'''?? '___') FROM DUAL;
?????????
??????1???ж???????????????
????SELECT TRANSLATE('ABC123'??'#1234567890.'??'#') FROM DUAL;
??????2????????E????????
????SELECT LENGTHB(TRANSLATE('ABCDEFGEFGDBE'??'E'||'ABCDEFGEFGDBE'??'E')) FROM DUAL;
????3??ROUND()????

????????????????????????ROUND()??????????????????????????ROUND???????е?????????????????и????????????TRUNC()?????????
?????磺SELECT ROUND(SYSDATE??'yyyy') FROM DUAL;
????SELECT ROUND(SYSDATE??'MM') FROM DUAL;
????SELECT ROUND(SYSDATE??'HH24') FROM DUAL;
????4??NVL??????
????NVL?????????:NVL(expr1??expr2)??NVL2(expr1??expr2??expr3)??NULLIF(expr1??expr2)??DECODE(expr1??expr2??value1??expr3??value2...??default)
????(1) NVL(expr1??expr2) :???expr1????????expr2???滻??
????(2) NVL2(expr1??expr2??expr3) :???expr1????????expr2????????expr3??
????(3) NULLIF(expr1??expr2):??expr1??expr2?????????????????null????????expr1??
????(3) DECODE(expr1??expr2??value1??expr3??value2...??default):???expr1??expr2????????value1?????expr1??expr3????????value2??...????????default??
????5??????????????
?????????????????????к????? (1) ANALYZE  (2) DBMS_STATS

????????????????????????????????
?????????????з?????
????ANALYZE TABLE TABLE_NAME COMPUTE STATISTICS;
????????ORACLE??????????????????DBMS_STATS?????к?????????????SCHEMA??TABLE??INDEX??????????????????????
????EXEC DBMS_STATS.GATHER_TABLE_STATS(OWNNAME=>'SCOTT'??TABNAME=>'EMP'??DEGREE=>4??CASCADE=>'TRUE');