创建视图语句中的 Counting/totaling 行，mysql

Question

我有一个数据库，我想创建一个视图，允许用户调用视图名称来查看视图的 "year, semester, credits"。我想要做的是让它给我年份，然后是学期，然后是每学期的总学分。

所以，如果我在 spring 2010 年有 2 个学生，并且他们每个 class 在 3 个学分时每个 class 上了 2 classes，那么结果应该是 return总共12个学分，以此类推第四。

EX。 '2010 Spring 12'

CREATE VIEW tot_cred26
AS
SELECT DISTINCT year, semester, COUNT(credits)
FROM course INNER JOIN takes;

再次感谢大家，SQL 的超级新手，你们真的很有帮助！ :)

Answer 1

下面的代码可能会解决问题：

CREATE VIEW tot_cred26
AS
SELECT year, semester, COUNT(credits) total_credits
FROM course INNER JOIN takes
group by year, semester
;

Answer 2

使用GROUP BY 合并每组值的行。既然你想要总学分，你应该使用 SUM; COUNT 只是计算行数。而您的 INNER JOIN 需要一个 ON 子句来指定两个表的关联方式；我假设两个表中都有一个 courseid 列。

CREATE VIEW tot_cred26 AS
SELECT year, semester, SUM(credits) as total_credits
FROM course AS c
INNER JOIN takes as t ON t.courseid = c.courseid
GROUP BY year, semester

创建视图语句中的 Counting/totaling 行，mysql

Counting/totaling rows in a create view statement, mysql

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