ORACLE数据库-函数

函数

单行函数：

从表中查询的每一行只返回一个值，可出现在select子句，where子句中

SELECT upper('smith') FROM DUAL
SELECT lower('HELLO WORLD') FROM DUAL
SELECT INITCAP('hello world') FROM DUAL--单词首字母大写
/*LPAD */
/*LTRIM */
UPDATE PVDTA.F4095 SET MLMCU=LPAD(TRIM(MLMCU),12,' ') 

日期函数

日期函数
数字函数

SELECT ROUND(34.6) FROM DUAL--四舍五入
SELECT TRUNC(34.6) FROM DUAL--截断小数

字符函数

SELECT SUBSTR('abcdefg',0,3) from dual/*从第0位开始，截取3位*/
select REPLACE('abcdefghicde','cde','xxx') from DUAL
SELECT MLMCU,LENGTH(MLMCU) FROM F4095--获取字段的长度

SELECT LTRIM(' ADD ')FROM DUAL--左去空格
SELECT RTRIM(' ADD ')FROM DUAL--右去空格
SELECT TRIM(' ADD ')FROM DUAL--左右去空格

SELECT LpaD('55',5,'0') from dual;--左补
select rpad('55',5,'0') FROM DUAL;--右补
/*第三个参数缺省时默认为是补充空格*/
select lpad('55',5) FROM DUAL

转换函数：

ToChar(),ToDate(),ToNumber()

其他函数:

Nvl(exp1,exp2):表达式一为null时，返回表达式二
Nvl2(exp1,exp2,exp3):表达式一为null时返回表达式三，否则返回表达式二
Nullif(exp1,exp2):两表达式相等时，返回null，否则返回表达式一

分组函数：基于一组行来返回

Avg,Min,Max,Sum,Count
Group by,having

分析函数

Row_number,rank,dense_rank
示例：

CREATE TABLE FA (
AID NUMBER ,
SCHOOL NUMBER,
FACILITY NUMBER,
QUALITY NUMBER
)
ALTER TABLE FA ADD PRIMARY KEY (AID)
ALTER TABLE FA ADD DES NCHAR(20)
SELECT * FROM FA FOR UPDATE

/*1. ROW_NUMBER() OVER(PARTITION BY COL1 ORDER BY COL2)*/

SELECT * FROM (SELECT AID,SCHOOL,DES,FACILITY,QUALITY,QUALITY_EX,ROW_NUMBER() OVER 
(PARTITION BY SCHOOL ORDER BY FACILITY) RN FROM FA )

SELECT * FROM (SELECT AID,SCHOOL,DES,FACILITY,QUALITY,QUALITY_EX,ROW_NUMBER() OVER 
(PARTITION BY SCHOOL ORDER BY FACILITY) RN FROM FA ) where RN=1
/*对于筛选某些字段重复的记录可用此方法*/

/*2.RANK() OVER(PARTITION BY COL1 ORDER BY COL2)跳跃排序*/
SELECT * FROM (SELECT AID,SCHOOL,DES,FACILITY,QUALITY,QUALITY_EX,RANK() OVER 
(PARTITION BY SCHOOL ORDER BY QUALITY) RN FROM FA )

/*由查询结果可知，相同的并列，下一个则跳跃到并列所替的序列后：如有两个并列2，那么下一个则直接排为4，跳过3；*/

/*3.RANK() OVER(PARTITION BY COL1 ORDER BY COL2)跳跃排序*/
SELECT * FROM (SELECT AID,SCHOOL,DES,FACILITY,QUALITY,QUALITY_EX,DENSE_RANK() OVER 
(PARTITION BY SCHOOL ORDER BY QUALITY) RN FROM FA )

--------由查询结果可知，当两个并列为2时，下一个仍连续有序为3，不跳跃到4