--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;
貌似只有Oracle提供该函数,而且不支持ANSI SQL,语法上也没CASE WHEN清晰,个人不推荐使用。
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%')
这种方法也是在特殊情况下使用,要多注意逻辑,不要弄错。
2.https://dba.stackexchange.com/questions/1170/oracle-sql-case-in-a-where-clause