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1、一、数学函数1.绝对值S:selectabs(-1)valueO:selectabs(-1)valuefromdual 2.取整(大)S:selectceiling(-1.001)valueO:selectceil(-1.001)valuefromdual 3.取整（小）S:selectfloor(-1.001)valueO:selectfloor(-1.001)valuefromdual 4.取整（截取）S:selectcast(-1.002asint)valueO:selecttrunc(-1.002)valuefromdual 5.四舍五入S:selectround(1.23
2、456,4)value1.23460O:selectround(1.23456,4)valuefromdual1.2346 6.e为底的幂S:selectExp(1)value2.7182818284590451O:selectExp(1)valuefromdual2.71828182 7.取e为底的对数S:selectlog(2.7182818284590451)value1O:selectln(2.7182818284590451)valuefromdual;1 8.取10为底对数S:selectlog10(10)value1O:selectlog(10,10)valuefro
3、mdual;1 9.取平方S:selectSQUARE(4)value16O:selectpower(4,2)valuefromdual16 10.取平方根S:selectSQRT(4)value2O:selectSQRT(4)valuefromdual2 11.求任意数为底的幂S:selectpower(3,4)value81O:selectpower(3,4)valuefromdual81 12.取随机数S:selectrand()valueO:selectsys.dbms_random.value(0,1)valuefromdual; 13.取符号S:selectsign(-
4、8)value-1O:selectsign(-8)valuefromdual-1 14.圆周率S:SELECTPI()value3.1415926535897931O:selectacos(-1)PIfromdual;selectexp(1)efromdual; 15.sin,cos,tan参数都以弧度为单位例如：selectsin(PI()/2)value得到1（SQLServer）16.Asin,Acos,Atan,Atan2返回弧度17.弧度角度互换(SQLServer，Oracle未知)DEGREES：弧度-〉角度RADIANS：角度-〉弧度二、数值间比较18.求集合最大值
5、S:selectmax(value)valuefrom(select1valueunionselect-2valueunionselect4valueunionselect3value)aO:selectgreatest(1,-2,4,3)valuefromdual 19.求集合最小值S:selectmin(value)valuefrom(select1valueunionselect-2valueunionselect4valueunionselect3value)aO:selectleast(1,-2,4,3)valuefromdual 20.如何处理null值(F2中的nul
6、l以10代替)S:selectF1,IsNull(F2,10)valuefromTblO:selectF1,nvl(F2,10)valuefromTbl 21.求字符序号S:selectascii(''a'')valueO:selectascii(''a'')valuefromdual 22.从序号求字符S:selectchar(97)valueO:selectchr(97)valuefromdual 23.连接S:select''11''+''22''+''33''valueO:selectCONCAT(''11'',''22'')33valuefromdual 23.子串位置-
7、-返回3S:selectCHARINDEX(''s'',''sdsq'',2)valueO:selectINSTR(''sdsq'',''s'',2)valuefromdual 23.模糊子串的位置--返回2,参数去掉中间%则返回7S:selectpatindex(''%d%q%'',''sdsfasdqe'')valueO:oracle没发现，但是instr可以通过第四个参数控制出现次数selectINSTR(''sdsfasdqe'',''sd'',1,2)val
