---------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
----------数学函数
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
--------数值间比较
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
26.子串全部替换
S:没发现
O:select Translate(fasdbfasegas,fa,我 ) value from dual
27.长度
S:len,datalength
O:length
28.大小写转换 lower,upper
29.单词首字母大写
S:没发现
O:select INITCAP(abcd dsaf df) value from dual
30.左补空格（LPAD的第一个参数为空格则同space函数）
S:select space(10)+abcd value
O:select LPAD(abcd,14) value from dual
31.右补空格（RPAD的第一个参数为空格则同space函数）
S:select abcd+space(10) value
O:select RPAD(abcd,14) value from dual
32.删除空格
S:ltrim,rtrim
O:ltrim,rtrim,trim
33. 重复字符串
S:select REPLICATE(abcd,2) value
O:没发现
34.发音相似性比较(这两个单词返回值一样，发音相同)
S:SELECT SOUNDEX (Smith), SOUNDEX (Smythe)
O:SELECT SOUNDEX (Smith), SOUNDEX (Smythe) from dual
SQLServer中用SELECT DIFFERENCE(Smithers, Smythers) 比较soundex的差
返回0-4，4为同音，1最高
--------------日期函数
35.系统时间
S:select getdate() value
O:select sysdate value from dual
36.前后几日
直接与整数相加减
37.求日期
S:select convert(char(10),getdate(),20) value
O:select trunc(sysdate) value from dual
select to_char(sysdate,yyyy-mm-dd) value from dual
38.求时间
S:select convert(char(8),getdate(),108) value
O:select to_char(sysdate,hh24:mm:ss) value from dual