ORACLE SQL单行函数（三）【weber出品必属精品】

16.L:代表本地货币符，这个和区域有关。这个时候我们想来显示一下人民币的符号：￥

$ vi .bash_profile       ---写入如下内容：

export NLS_LANG='SIMPLIFIED CHINESE'_CHINA.AL32UTF8   ---修改成简体中文+地区+字符集

source .bash_profile       ---让环境变量生效

[oracle@oracle ~]$ sqlplus scott/tiger

SQL*Plus: Release 10.2.0.5. - Production on 星期五 8月  :: 

Copyright (c) , , Oracle.  All Rights Reserved.

Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.5. - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL>---如果你是用x-shell或者putty远程连接linux的话，需要将你的客户端的字符集也改回来

17.TO_NUMBER:将一个字符串转化为数字

把十进制转换为十六进制：（to_char）

SQL> select to_char(,'xxx') from dual;

TO_CHAR(,'
------------
   a

把十六进制转换为十进制：（to_number）

SQL> select to_number('a','xxx') from dual;

TO_NUMBER('A','XXX')
--------------------
          

18.日期的两位表示方式：RR和YY

SQL> select * from emp where hiredate=to_date('17-12-80','dd-mm-rr');

EMPNO ENAME  JOB         MGR HIREDATE              SAL       COMM DEPTNO
----- ------ --------- ----- ------------------- ----- ---------- ------
  SMITH  CLERK       -- ::                   

日期的两位表示方式：RR和YY

YY:始终与当前世纪一致

RR：得到的是与当前年最近的年份

 19.操作NULL值的函数

NVL(expr1, expr2)

如果expr1为null,则返回expr2,否则返回expr1

可以使用的数据类型是数字、日期、字符型.

数据类型必须能够匹配（expr1和expr2的类型必须要一致）

SQL> select ename ,comm,nvl(comm,) nvl from emp;

ENAME                    COMM    NVL
------------------------------ ---------- ----------
SMITH
ALLEN
WARD
JONES
MARTIN                       

20.NVL(expr1, expr2，expr2)

如果expr1非空，就返回expr2

如果expr1为空，就返回expr3

SQL> select ename,sal,comm,sal+comm,sal+nvl(comm,),nvl2(comm,'工资加奖金','纯工资') "收入类别" from emp;

ENAME    SAL       COMM   SAL+COMM SAL+NVL(COMM,) 收入类别
------ ----- ---------- ---------- --------------- ---------------
SMITH                                        纯工资
ALLEN                               工资加奖金
WARD                                工资加奖金
JONES                                      纯工资
MARTIN                             工资加奖金
BLAKE                                      纯工资
CLARK                                      纯工资
SCOTT                                      纯工资
KING                                       纯工资
TURNER                                工资加奖金
ADAMS                                      纯工资
JAMES                                        纯工资
FORD                                       纯工资
MILLER                                     纯工资

21.NULLIF(expr1,expr2)

如果expr1和expr2相同就返回空，否则返回expr1

SQL> select ename,nullif(ename,'KING') from emp;

ENAME  NULLIF(ENAME,'KING')
------ ------------------------------
SMITH  SMITH
ALLEN  ALLEN
WARD   WARD
JONES  JONES
MARTIN MARTIN
BLAKE  BLAKE
CLARK  CLARK
SCOTT  SCOTT
KING
TURNER TURNER
ADAMS  ADAMS
JAMES  JAMES
FORD   FORD
MILLER MILLER

22. COALESCE(expr1,expr2,expr3,…exprn)：返回括号内第一个非空的值

23.条件表达式函数

decode与case when

区别：

1. decode是oracle自己的函数，case when是SQL99标准函数

2. decode只能进行等值判断，case when可以进行非等值判断

​SQL> select ename,job,case job when 'CLERK' then '1.clerk'
     when 'SALESMAN' then '2.saleman'
          else 'other'  end
          from emp

ENAME  JOB   CASEJOBWHEN'CLERK'THEN'1.CL
------ --------- ---------------------------
SMITH  CLERK     .clerk
ALLEN  SALESMAN  .saleman
WARD   SALESMAN  .saleman
JONES  MANAGER   other
MARTIN SALESMAN  .saleman
BLAKE  MANAGER   other
CLARK  MANAGER   other
SCOTT  ANALYST   other
KING   PRESIDENT other
TURNER SALESMAN  .saleman
ADAMS  CLERK     .clerk
JAMES  CLERK     .clerk
FORD   ANALYST   other
MILLER CLERK     .clerk

decode用法实例

SQL> select ename,decode(job,'SALESMAN','CLERK','UNKNOWN') from emp;

ENAME  DECODE(JOB,'SALESMAN'
------ ---------------------
SMITH  UNKNOWN
ALLEN  CLERK
WARD   CLERK
JONES  UNKNOWN
MARTIN CLERK
BLAKE  UNKNOWN
CLARK  UNKNOWN
SCOTT  UNKNOWN
KING   UNKNOWN
TURNER CLERK
ADAMS  UNKNOWN
JAMES  UNKNOWN
FORD   UNKNOWN
MILLER UNKNOWN

使用case when进行非等值判断：

SQL> select ename,sal,case when sal between  and  then
when sal between  and  then
when sal between  and  then
when sal between  and  then
else  end grade from emp

ENAME         SAL      GRADE
------ ---------- ----------
SMITH
ALLEN
WARD
JONES
MARTIN
BLAKE
CLARK
SCOTT
KING
TURNER
ADAMS
JAMES
FORD
MILLER             

24.函数的嵌套

单行的函数可以嵌套到任何一个层次

嵌套函数的计算顺序——先计算深层嵌套，再计算浅层嵌套.

SQL> select ename,mgr,nvl(to_char(mgr),'no manager') from emp;

ENAME    MGR NVL(TO_CHAR(MGR),'NOMANAGER')
------ ----- ----------------------------------------
SMITH
ALLEN
WARD
JONES
MARTIN
BLAKE
CLARK
SCOTT
KING         no manager
TURNER
ADAMS
JAMES
FORD
MILLER