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

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

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

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, -- 别名命名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;  

select decode(sex, 'M', 'Male', 'F', 'Female', 'Unknown') from   employees;

SELECT T2.*, T1.*    FROM T1, T2   WHERE (T2.COMPARE_TYPE = 'A' AND T1.SOME_TYPE LIKE 'NOTHING%')          OR         (T2.COMPARE_TYPE != 'A' AND T1.SOME_TYPE NOT LIKE 'NOTHING%')