oracle函数之decode的使用

语法：

decode(条件,值1,返回值1,值2,返回值2,...值n,返回值n,缺省值)

decode(字段或字段的运算,值1,值2,值3) 

select decode(value,<if this value>,<return this value>) from table

这个函数运行的结果是，当字段或字段的运算的值等于值1时，返回值2，否则返回值3 ；

值1...值n也可以使表达式，这个函数使得某些sql语句简单了好多

使用方法1：比较大小

select decode(sign(变量1-变量2),-1,变量1,变量2) from dual;

sign()函数根据某个值是0,正数,负数，分别返回0,1,-1

 使用方法二：相当于IF-THEN- ELSIF-THEN-...ELSE-END IF

如果我们想统计一张表中男女生的数量，常规做法是：

select  count(1) from table_name where sex='男'

union

select  count(1)  from table_name where sex='女'

使用decode则只需要一句话：

select  sum(decode(sex,'男',1,0) as '男',decode(sex,'女',1,0) as '女') from table_name;

实例：

 SELECT O1.ORG_NAME S_NAME,
            O1.ORG_ID S_ID,             
            SUM(DECODE(R1.REJECT_REASON, '1', 1, 0)) AS WZZH,
            SUM(DECODE(R1.REJECT_REASON, '2', 1, 0)) AS AQCSBZ,
            SUM(DECODE(R1.REJECT_REASON, '3', 1, 0)) AS WBGZXKSX,
            SUM(DECODE(R1.REJECT_REASON, '4', 1, 0)) AS WXCAQJD,
            SUM(DECODE(R1.REJECT_REASON, '5', 1, 0)) AS WAQFH,
            SUM(DECODE(R1.REJECT_REASON, '6', 1, 0)) AS FSGCL,
            SUM(DECODE(R1.REJECT_REASON, '7', 1, 0)) AS FDYCZ,
            SUM(DECODE(R1.REJECT_REASON, '8', 1, 0)) AS YSTSD,
            SUM(DECODE(R1.REJECT_REASON, '9', 1, 0)) AS TDSBGZ,
            SUM(DECODE(R1.REJECT_REASON, '10',1, 0)) AS BHGGJ,
            SUM(DECODE(R1.REJECT_REASON, '11',1, 0)) AS BHGSB,
            SUM(DECODE(R1.REJECT_REASON, '12',1, 0)) AS CSTZZY,
            SUM(DECODE(R1.REJECT_REASON, '13',1, 0)) AS JHJS,
            SUM(DECODE(R1.REJECT_REASON, '14',1, 0)) AS QT      
       FROM TOP_ORGANIZATION O1 
       LEFT JOIN (SELECT R.REJECT_REASON,
                         O2.ORG_CODE
                 FROM SP_SS_EMPLOYEE_REJECT R,TOP_ORGANIZATION O2
                 WHERE R.REPORT_DEPARTMENT_OID = O2.ORG_ID                 
                ) R1
       ON R1.ORG_CODE LIKE O1.ORG_CODE||'%'
       WHERE O1.PARENT_ORG_ID = 
       GROUP BY O1.ORG_ID,O1.ORG_NAME