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--字符串從前面取三個(0開始)
select Name,substr(Name,0,3) from t1;
--字符串從后面取三個
select Name,substr(Name,-3,3),length(Name) 串長度 from t1;

SELECT ASCII('A'),ASCII('B') from dual;

select CHR(100),CHR(80) from dual;

select CONCAT(CHR(65),CONCAT(CHR(67),CHR(98))) from dual;

select CHR(65)||CHR(66)||CHR(76) from dual;

--將每個單詞的第一個字母大寫其它字母小寫返回。
select INITCAP('substr,abc,substring') from dual;
--返回i在MISSISSIPPI中第3次出現(xiàn)的位置，
select INSTR('Mississippi','i',5,3) from dual;
select INSTR('Mississippi','i',-2,3) from dual;
--返回的是字節(jié)
select INSTRB('Mississippi','i',5,3) from dual;
select INSTRB('Mississippi','i',-2,3) from dual;
--長度
select length('WHO ARE YOU') from dual;
select nvl(null,'空') from dual;
--小寫
select lower('WHo are You') from dual;
--LPAD左側(cè)用字符串補(bǔ)足到一定長度
select LPAD('DFSDf................',9,'WHO') from dual;
select LPAD('DFSD',9,'WHO') from dual;
select LPAD('DFSD',9,'') from dual;
select LPAD('DFSD',length('DFSD')+length('WHO......'),'WHO......') from dual;
--把最左邊的字符去掉，使其第一個字符不在其中
select ltrim('Mississippi','Mis') from dual;
select ltrim('Mississippi','miD') from dual;
--RPAD右側(cè)用字符串補(bǔ)足到一定長度
select RPAD('DFSDf................',9,'WHO') from dual;
select RPAD('DFSD',9,'WHO') from dual;
select RPAD('DFSD',9,'') from dual;
select RPAD('DFSD',length('DFSD')+length('WHO......'),'WHO......') from dual;
--把最右邊的字符去掉，使其第一個字符不在其中
select Rtrim('Mississippi','Mis') from dual;
select Rtrim('Mississippi','miD') from dual;
--替換
select REPLACE('uptown','up','down') from dual;
--substr和substrb
select SUBSTR('Message',1,4) from dual;
select SUBSTR('ABCDEFG',5) from dual;
select substrb('國際勞動節(jié)國營農(nóng)場',5) from dual;
select substrb('國際勞動節(jié)國營農(nóng)場',2) from dual;
select substrb('國際勞動節(jié)國營農(nóng)場',4,8) from dual;
select substrb('國際勞動節(jié)國營農(nóng)場',3,8) from dual;
--發(fā)音
select SOUNDEX('dawes') Dawes,SOUNDEX('daws') Daws, SOUNDEX('dawson') from dual;
--translate
select TRANSLATE('ABCDefghijklmn','eg','替代') test from dual;

select TRIM(' Space padded   0..o0.. ') trim from dual;

select UPPER('abDCCfasdfsdafasdf') from dual;

--【數(shù)學(xué)函數(shù)】所有函數(shù)都有數(shù)字參數(shù)并返回數(shù)字值。所有三角函數(shù)的操作數(shù)和值都是弧度而不是角度，
--oracle沒有提供內(nèi)建的弧度和角度的轉(zhuǎn)換函數(shù)。
select abs(-10.234) from dual;
select acos(-1),acos(1) from dual;
select asin(1),asin(0) from dual;
select atan(1),atan(-1) from dual;
select ceil(-2),ceil(5.1) from dual;
select cos(-1) from dual;
select cosh(1) from dual;
select exp(3),exp(2),exp(1) from dual;
select Floor(-3.2),floor(5.91) from dual;
select LN(2) from dual;
select Log(10,2),log(2,10),log(10,1000) from dual;
select MOD(19,3),MOD(20,3),MOD(21,3) from dual;
select POWER(3,4),POWER(4,2) from dual;
select ROUND(12345,-2),ROUND(12345.54321,2),ROUND(-234234.9800234) FROM dual;
select SIGN(-10),SIGN(0),SIGN(1000) from dual;
select sin(1.57) from dual;
select sinh(2.34) from dual;
select SQRT(2),sqrt(3) from dual;
select TAN(1.2) from dual;
select TANH(2.32) from dual;
select trunc(2.2342342,5),trunc(2.3234234) from dual;

--【日期函數(shù)】操作DATE數(shù)據(jù)類型，絕大多數(shù)都有DATE數(shù)據(jù)類型的參數(shù)
--增加月
select sysdate,Add_MONTHS(sysdate,1),
Add_MONTHS(TO_Date('2008-05-31 18:18:18','yyyy-MM-dd HH24:MI:SS'),1),
Add_MONTHS(TO_Date('2008-05-31 18:18:18','yyyy-MM-dd HH24:MI:SS'),2)
from dual;
--每月最后一天 只區(qū)別了日期, 時間沒有區(qū)別
select Last_day(sysdate) from dual;
--如果d1和d2的日的日期都相同，或者都使該月的最后一天，那么將返回一個整數(shù)，否則會返回的結(jié)果將

包含一個分?jǐn)?shù)。
select MONTHS_BETWEEN(sysdate,To_Date('2008-05-31 14:40:00','yyyy-MM-dd HH24:MI:SS')) from

dual;

select NEW_TIME(sysdate,'GMT','PST') from dual;

select NEXT_DAY(To_Date('2007-06-04','yyyy-MM-dd'),'Monday') "1st Monday"
from dual;

select ROUND(sysDate,'yyyy'),ROUND(sysDate,'mm'),ROUND(sysdate,'dd'),
        ROUND(sysdate,'HH24'),ROUND(sysDate,'MI')
from dual;
select sysdate from dual;

select trunc(sysdate),trunc(sysdate,'HH24'),trunc(sysdate,'MI') from dual;