參考文件：http://www.cnblogs.com/eshizhan/archive/2012/04/06/2435493.html

<span style="font-size:18px;">-- nvl函式
--　NVL( string1, replace_with)　　功能：如果string1為NULL，則NVL函式返回replace_with的值，否則返回string1的值。

select nvl(flag,'11')flag from t_operation_log

-- nvl2函式
-- 　NVL2(E1, E2, E3)的功能為：如果E1為NULL，則函式返回E3，若E1不為null，則返回E2。
select nvl2(flag,'11','22')flag from t_operation_log
-- decode 函式
--decode(條件,值1,翻譯值1,值2,翻譯值2,...值n,翻譯值n,預設值)

select flag,decode(flag,'1','成功','0','失敗') flagchina from t_operation_log</span>
 

--第一中寫法
select flag, (
case flag when '1' then '成功'
       when '0' then '失敗'
       else '其它'
       end ) chinaflag
from t_operation_log

-- 第二種寫法
 select flag, (
 case when flag='1' then '成功' 
 when flag='0' then '失敗'
 else '其它'
 end
 ) chinaflag from t_operation_log

 CASE WHEN 在語句中不同位置的用法

2.1 SELECT CASE WHEN 用法

SELECT   grade, COUNT (CASE WHEN sex = 1 THEN 1      /*sex 1為男生，2位女生*/
                       ELSE NULL
                       END) 男生數,
                COUNT (CASE WHEN sex = 2 THEN 1
                       ELSE NULL
                       END) 女生數
    FROM students GROUP BY
 
 grade;

2.3 WHERE CASE WHEN 用法

SELECT T2.*, T1.*
   FROM T1, T2
  WHERE (CASE WHEN T2.COMPARE_TYPE = 'A' AND
                   T1.SOME_TYPE LIKE 'NOTHING%'
                THEN 1
              WHEN T2.COMPARE_TYPE != 'A' AND
                   T1.SOME_TYPE NOT LIKE 'NOTHING%'
                THEN 1
              ELSE 0
           END) = 1

2.4 GROUP BY CASE WHEN 用法

SELECT  
CASE WHEN salary <= 500 THEN '1'  
WHEN salary > 500 AND salary <= 600  THEN '2'  
WHEN salary > 600 AND salary <= 800  THEN '3'  
WHEN salary > 800 AND salary <= 1000 THEN '4'  
ELSE NULL END salary_class, -- 別名命名COUNT(*)  
FROM    Table_A  
GROUP BY  
CASE WHEN salary <= 500 THEN '1'  
WHEN salary > 500 AND salary <= 600  THEN '2'  
WHEN salary > 600 AND salary <= 800  THEN '3'  
WHEN salary > 800 AND salary <= 1000 THEN '4'  
ELSE NULL END;