oracle case
Oracle CASE WHEN 用法介绍1. CASE WHEN 表达式有两种形式[url=]
[/url]
--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 [url=][/url]
2. CASE WHEN 在语句中不同位置的用法2.1 SELECT CASE WHEN 用法[url=]
[/url]
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;[url=]
[/url]
2.3 WHERE CASE WHEN 用法[url=]
[/url]
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[url=]
[/url]
2.4 GROUP BY CASE WHEN 用法[url=]
[/url]
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; [url=]
[/url]
3.关于IF-THEN-ELSE的其他实现3.1 DECODE() 函数select decode(sex, 'M', 'Male', 'F', 'Female', 'Unknown')
from employees;
3.2 在WHERE中特殊实现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%')
[/url]--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 [url=]
[/url]2. CASE WHEN 在语句中不同位置的用法2.1 SELECT CASE WHEN 用法[url=]
[/url]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;[url=]
[/url]2.3 WHERE CASE WHEN 用法[url=]
[/url]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[url=]
[/url]2.4 GROUP BY CASE WHEN 用法[url=]
[/url]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; [url=]
[/url]3.关于IF-THEN-ELSE的其他实现3.1 DECODE() 函数select decode(sex, 'M', 'Male', 'F', 'Female', 'Unknown')
from employees;
3.2 在WHERE中特殊实现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。
来自 “ ITPUB博客 ” ，链接：https://blog.itpub.net/31349667/viewspace-2123213/ ，如需转载，请注明出处，否则将追究法律责任。
请登录后发表评论
登录
全部评论
