sql 函數

表：create table T_Person (FidNumber varchar(20),Fname varchar(20),FbrithDay datetime,
    FregDay datetime,Fweight decimal(10,2));

 

求絕對值：select Fweight-50,abs(Fweight-50),abs(-5.03) from t_person;

求冪函數：select Fweight,power(Fweight,-0.5),power(Fweight,2) from t_person;第二個參數爲冪。

求平方根：select fweight,sqrt(fweight) from t_person;

求隨機：mysql：select rand();

sqlserver：select rand(1234);

oracle：select dbms_random.value(10,50) from dual;>=10,<50;

select dbms_random.normal from dual;

select dbms_random.string(opt,len) from dual;

DB2:select SYSFUN.rand() from SYSIBM.SYSDUMMY1;

舍入最大值：select Fname,fweight,ceiling(fweight),ceil(fweight *-1) from t_person;

舍入最小值：select Fname,fweight,floor(fweight),floor(fweight *-1)from t_person;

四捨五入：select Fname,fweight,round(fweight,1),round(fweight *-1,0),round(fweight,-1) from t_person;後面一位是精度，可爲負。

弧度轉換爲角度：mysql，server：select fname ,fweight,degrees(fweight) from t_person;

Oracle，db2：select fname ,fweight,(Fweight*180)/acos(-1) from t_person;
角度轉弧度：select fname ,fweight,(Fweight*acos(-1))/180 from t_person;     select fname ,fweight,radians(fweight) from t_person;

求符號：select fname ,fweight,sign(Fweight) from t_person;大於0得1，<0=-1,=0=0;

 求發音差別：select soundex('jack'),soundex('jeck') from dual;
select fname,soundex(fname) from t_person;
db2，server有函數（1到4）來判斷髮音區別：select difference (fname,'merry') from t_person;

mysql求時間：select now(),sysdate(),current_date(),current_timestamp(),current_time();

server：求時間：select convert(varchar(50),getdate(),101) as riqi;
select convert(varchar(50),getdate(),108) as sj;

oracle：select to_char(sysdate(),'YYYYMMDD') from dual;

db2：select current timestamp/date/time from sysibm.sysdummyl;

日期加法：mysql：select fbrithday,date_add(fbrithday,interval 1 week) as wk,
date_add(fbrithday,interval 2 month) as mon,
date_add(fbrithday,interval 5 quarter) as week from t_person；

 server：dateadd(datepart,number,date)；

Oracle：用+，-計算時間天數，addmonths（date，number）計算月

db2：date+length   unit(單位：day，month，year)

類型轉換：mysql：select cast('-30' as signed) as sig,
　　　　　　　　　　convert('36',unsigned) as usig；

sqlserver：convert（類型，轉換值）與上面相反；Oracle與db2有專門類型轉換函數。o：to_date(exp,format),to_char(exp,format)...;2:date(),int()。

 

空值轉換：select fbrithday,fregday, coalesce(fbrithday,fregday,'2018-08-08') from t_person；從第一個參數開始判斷是否爲空，不爲空則賦這個值。

簡化版：M:IFNULL(EXP,VALUE),S:ISNULL(E,V),O:NVL(E,V);

 

偲