Oracle中case when函数的用法

SELECT grade, COUNT (CASE WHEN sex = 1 THEN 1   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 keyCol, CASE WHEN keyCol IN ( SELECT keyCol FROM tbl_B )  THEN 'Matched' ELSE 'Unmatched' END Label 
FROM tbl_A;

UPDATE PersonnelSET salary =
CASE WHEN salary >= 5000  　                THEN salary * 0.9 
     WHEN salary >= 2000 AND salary < 4600  THEN salary * 1.15 
ELSE salary END;

SELECT * FROM   TB_Test
WHERE  stateid IN ( 10, 20 )
       AND ( CASE  WHEN stateid = 20 AND userid <> 2 THEN 0
                   ELSE 1 
              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' 
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' 
ELSE NULL END;