--简单Case函数  
 
CASE sex  
WHEN '1' THEN 男'  
2女ELSE 其他END  
 
Case搜索函数  CASE
WHEN sex = END  

SELECT   grade,COUNT (CASE = 1 THEN 1      /*sex 1为男生，2位女生*/
                       ELSE NULL
                       END) 男生数,0)">2 1
                       NULL
                       END) 女生数
    FROM students GROUP BY grade;

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

SELECT  
WHEN salary <= 500 > 500 AND salary 600  600 800  3800 1000 4NULL END salary_class, 别名命名
COUNT(*)  
FROM    Table_A  
BY  
END;  

select decode(sex,0)">M',0)">MaleFFemaleUnknown')
from   employees;

WHERE (T2.COMPARE_TYPE AND T1.SOME_TYPE ')
         OR
        (T2.COMPARE_TYPE ')