时间：2022-07-17 09:13:42 | 栏目：Oracle | 点击：次
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;
Case函数不同于DECODE函数。在Case函数中，可以使用BETWEEN,LIKE,IS NULL,IN,EXISTS等等。比如说使用IN,EXISTS，可以进行子查询，从而 实现更多的功能。
SELECT keyCol, CASE WHEN keyCol IN ( SELECT keyCol FROM tbl_B ) THEN 'Matched' ELSE 'Unmatched' END Label FROM tbl_A;
也可以使用NOT IN和NOT EXISTS，但是这个时候要注意NULL的情况。
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;