SQL Server、Oracle、MySQL和Vertica数据库常用函数对比 Vertica数据库是HP公司新收购的用于BI方面的数据库。
绝对值 S:select abs(-1) value O:select abs(-1) value from dual M:select abs(-1) value from dual V:select abs(-1) 向上取整 S:select ceiling(-1.001) value O:select ceil(-1.001) value from dual M:select ceil(-1.001) value from dual V:select ceil(-1.001) 向下取整 S:select floor(-1.001) value O:select floor(-1.001) value from dual M:select floor(-1.001) value from dual V:select floor(-1.001) 取整（截取） S:select cast(-1.002 as int) value O:select trunc(-1.002) value from dual V:select trunc(-1.002) 四舍五入 S:select round(1.23456,4) value 1.23460 O:select round(1.23456,4) value from dual 1.2346 M:select round(1.23456,4) value from dual 1.2346 V:select round(1.23456,4.0) e为底的幂 S:select Exp(1) value 2.71828182845905 O:select Exp(1) value from dual 2.71828182 M:select Exp(1) value from dual 2.718281828459045 V:select Exp(1.0) 2.71828182845905 取e为底的对数 S:select log(2.7182818284590451) value 1 O:select ln(2.7182818284590451) value from dual; 1 M:select ln(2.7182818284590451) value from dual; 1 V: select ln(2.7182818284590451) 1 取10为底对数 S:select log10(10) value 1 O:select log(10,10) value from dual; 1 M:select log(10,10) value from dual; 1 M: select log(10,10) 1 取平方 S:select SQUARE(4) value 16 O:select power(4,2) value from dual 16 M:select power(4,2) value from dual 16 V:select power(4,2) 16 取平方根 S:select SQRT(4) value 2 O:select SQRT(4) value from dual 2 M:select SQRT(4) value from dual 2 V:select SQRT(4) 2 求任意数为底的幂 S:select power(3,4) value 81 O:select power(3,4) value from dual 81 M:select power(3,4) value from dual 81 V:select power(3,4) 81 取随机数 S:select rand() value O:select sys.dbms_random.value(0,1) value from dual; M:select rand() value from dual; V:select random() 取符号 S:select sign(-8) value -1 O:select sign(-8) value from dual -1 M:select sign(-8) value from dual -1 V:select sign(-8) -1 圆周率 S:SELECT PI() value 3.14159265358979 O: SELECT ACOS(-1) FROM DUAL; M: SELECT ACOS(-1) FROM DUAL; 3.141592653589793 V: SELECT PI() 3.14159265358979数值间比较 15. 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 M:select greatest(1,-2,4,3) value from dual V:select greatest(1,-2,4,3) 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 M:select least(1,-2,4,3) value from dual V:select least(1,-2,4,3) 如何处理null值(F2中的null以10代替) Create table tbl (f1 varchar(10),f2 int); Insert into tbl(f1,f2) values(‘aa’,null); Insert into tbl(f1,f2) values(‘bb’,7); S:select F1,IsNull(F2,10) value from Tbl O:select F1,nvl(F2,10) value from Tbl M:select F1,ifnull(F2,10) value from Tbl V:select F1,IsNull(F2,10) value from Tbl 求字符ascii码 S:select ascii('a') value O:select ascii('a') value from dual M:select ascii('a') value from dual V:select ascii('a') 从ascii码求字符 S:select char(97) value O:select chr(97) value from dual M:select char(97) value from dual V:select chr(97) 连接字符串 S:select '11'+'22'+'33' value O:select CONCAT('11','22') 33 value from dual M:select concat('11','22','33') value V:select '11'||'22'||'33' 子串位置 –返回3 S:select CHARINDEX('s','sdsq',2) value O:select INSTR('sdsq','s',2) value from dual M:select LOCATE('s','sdsq',2) value from dual V:select INSTR('sdsq','s',2) 求子串 S:select substring('abcd',2,2) value O:select substr('abcd',2,2) value from dual M:select substr('abcd',2,2) value from dual V:select substr('abcd',2,2) 子串代替 返回aijklmnef S:SELECT STUFF('abcdef', 2, 3, 'ijklmn') value O:SELECT Replace('abcdef', 'bcd', 'ijklmn') value from dual M:SELECT Replace('abcdef', 'bcd', 'ijklmn') value from dual V:SELECT Replace('abcdef', 'bcd', 'ijklmn') 字符串长度 S:len,datalength O: select length('aaa') value from dual M: select length('aaa') value from dual V: select length('aaa '::CHAR(10)) Select length('aaa '::varchar(10)) select length('aaa') 大小写转换 lower,upper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 M:select LPAD('abcd',14, ' ') value from dual V:select LPAD('abcd',14, ' ') value from dual 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 M:select RPAD('abcd',14, ' ') value from dual V:select RPAD('abcd',14, ' ') value from dual 删除空格 S:ltrim,rtrim O:ltrim,rtrim,trim M:ltrim,rtrim,trim V:ltrim,rtrim,trim日期函数 29. 系统时间
S:select getdate() value O:select sysdate value from dual M:select now() value from dual V:select sysdate() select getdate() select now() 会显示时区 前后几日 S:直接与整数相加减 O:直接与整数相加减 M: select now()+interval 1 day value from dual V:直接与整数相加减 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 M:select DATE_FORMAT(NOW(),'%Y-%m-%d') value from dual; V:select to_char(sysdate(),'YYYY-MM-DD') 求时间 S:select convert(char(8),getdate(),108) value O:select to_char(sysdate,'hh24:mm:ss') value from dual M:select DATE_FORMAT(NOW(),'%T') value from dual V:select to_char(sysdate,'hh24:mi:ss') 取日期时间的其他部分 S:DATEPART 和 DATENAME 函数 （第一个参数决定） O:to_char函数 第二个参数决定 参数---------------------------------下表需要补充 year yy, yyyy quarter qq, q (季度) month mm, m (m O无效) dayofyear dy, y (O表星期) day dd, d (d O无效) week wk, ww (wk O无效) weekday dw (O不清楚) Hour hh,hh12,hh24 (hh12,hh24 S无效) minute mi, n (n O无效) second ss, s (s O无效) millisecond ms (O无效) M:date_format函数 第二个参数决定 格式 描述 %a 缩写星期名 %b 缩写月名 %c 月，数值 %D 带有英文前缀的月中的天 %d 月的天，数值(00-31) %e 月的天，数值(0-31) %f 微秒 %H 小时 (00-23) %h 小时 (01-12) %I 小时 (01-12) %i 分钟，数值(00-59) %j 年的天 (001-366) %k 小时 (0-23) %l 小时 (1-12) %M 月名 %m 月，数值(00-12) %p AM 或 PM %r 时间，12-小时（hh:mm:ss AM 或 PM） %S 秒(00-59) %s原地址：http://www.verydemo.com/demo_c152_i10134.html
