SQLServer和Oracle是大家经常用到的数据库，在此感谢作者总结出这些常用函数以供大家参考。
数学函数
1.绝对值
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（小）
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为底的幂
S:select Exp(1) value 2.7182818284590451
O:select Exp(1) value from dual 2.71828182
7.取e为底的对数
S:select log(2.7182818284590451) value 1
O:select ln(2.7182818284590451) value from dual; 1
8.取10为底对数
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.求任意数为底的幂
S:select power(3,4) value 81
O:select power(3,4) value from dual 81
12.取随机数
S:select rand() value
O:select sys.dbms_random.value(0,1) value from dual;
13.取符号
S:select sign(-8) value -1
O:select sign(-8) value from dual -1
14.圆周率
S:SELECT PI() value 3.1415926535897931
O:不知道
15.sin,cos,tan 参数都以弧度为单位
例如：select sin(PI()/2) value 得到1（SQLServer）
16.Asin,Acos,Atan,Atan2 返回弧度
17.弧度角度互换(SQLServer，Oracle不知道)
DEGREES：弧度-〉角度
RADIANS：角度-〉弧度
数值间比较
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.如何处理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.求字符序号
S:select ascii(''a'') value
O:select ascii(''a'') value from dual
22.从序号求字符
S:select char(97) value
O:select chr(97) value from dual
23.连接
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2,参数去掉中间%则返回7
S:select patindex(''%d%q%'',''sdsfasdqe'') value
O:oracle没发现，但是instr可以通过第四个参数控制出现次数
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
S:SELECT STUFF(''abcdef'', 2, 3, ''ijklmn'') value
O:SELECT Replace(''abcdef'', ''bcd'', ''ijklmn'') value from dual
