SQLServer和Oracle是大家經(jīng)常用到的數(shù)據(jù)庫，在此感謝作者總結出這些常用函數(shù)以供大家參考。
數(shù)學函數(shù)
1.絕對值
S:select abs(-1) value
O:select abs(-1) value from dual
2.取整(大)
S:select ceiling(-1.001) value
O:select ceil(-1.001) value from dual
3.取整（�。�
S:select floor(-1.001) value
O:select floor(-1.001) value from dual
4.取整（截取）
S:select cast(-1.002 as int) value
O:select trunc(-1.002) value from dual
5.四舍五入
S:select round(1.23456,4) value 1.23460
O:select round(1.23456,4) value from dual 1.2346
6.e為底的冪
S:select Exp(1) value 2.7182818284590451
O:select Exp(1) value from dual 2.71828182
7.取e為底的對數(shù)
S:select log(2.7182818284590451) value 1
O:select ln(2.7182818284590451) value from dual; 1
8.取10為底對數(shù)
S:select log10(10) value 1
O:select log(10,10) value from dual; 1
9.取平方
S:select SQUARE(4) value 16
O:select power(4,2) value from dual 16
10.取平方根
S:select SQRT(4) value 2
O:select SQRT(4) value from dual 2
11.求任意數(shù)為底的冪
S:select power(3,4) value 81
O:select power(3,4) value from dual 81
12.取隨機數(shù)
S:select rand() value
O:select sys.dbms_random.value(0,1) value from dual;
13.取符號
S:select sign(-8) value -1
O:select sign(-8) value from dual -1
14.圓周率
S:SELECT PI() value 3.1415926535897931
O:不知道
15.sin,cos,tan 參數(shù)都以弧度為單位
例如：select sin(PI()/2) value 得到1（SQLServer）
16.Asin,Acos,Atan,Atan2 返回弧度
17.弧度角度互換(SQLServer，Oracle不知道)
DEGREES：弧度-〉角度
RADIANS：角度-〉弧度
數(shù)值間比較
18. 求集合最大值
S:select max(value) value from
(select 1 value
union
select -2 value
union
select 4 value
union
select 3 value)a
O:select greatest(1,-2,4,3) value from dual
19. 求集合最小值
S:select min(value) value from
(select 1 value
union
select -2 value
union
select 4 value
union
select 3 value)a
O:select least(1,-2,4,3) value from dual
20.如何處理null值(F2中的null以10代替)
S:select F1,IsNull(F2,10) value from Tbl
O:select F1,nvl(F2,10) value from Tbl
21.求字符序號
S:select ascii('a') value
O:select ascii('a') value from dual
22.從序號求字符
S:select char(97) value
O:select chr(97) value from dual
23.連接
S:select '11'+'22'+'33' value
O:select CONCAT('11','22') 33 value from dual
23.子串位置 --返回3
S:select CHARINDEX('s','sdsq',2) value
O:select INSTR('sdsq','s',2) value from dual
23.模糊子串的位置 --返回2,參數(shù)去掉中間%則返回7
S:select patindex('%d%q%','sdsfasdqe') value
O:oracle沒發(fā)現(xiàn)，但是instr可以通過第四個參數(shù)控制出現(xiàn)次數(shù)
select INSTR('sdsfasdqe','sd',1,2) value from dual 返回6
24.求子串
S:select substring('abcd',2,2) value
O:select substr('abcd',2,2) value from dual
25.子串代替 返回aijklmnef
