是否存在“全部出现"? (设置除法?)MySQL内置的操作? [英] Is there a "appears in all" (set division?) operation built into MySQL?

问题描述

很抱歉这个简单的问题，但是我不知道正确的措词方式来获得有用的结果.我想知道MySQL中是否有支持全部"关系的函数.我指的是设置除法(当我在手册页中查找除法时，我只看到MySQL中的精确数学除法).因此，例如，如果我与学生和课程有联系，我可能想检索所有学生都参加的课程列表(也许，课程ID号出现在每个学生的下方，或类似的名称).我的问题有意义吗?我可以提出一个不同的查询来完成工作，但是如果我可以使用一个简单的内置函数来简化所有工作，那将是非常好的.

Sorry for the simple question, but I didn't know the proper way to word it to get useful results. I was wondering if there was a function in MySQL that supports a "has all" relationship. The term that I think I'm referring to is set division (when I look up division in the manual pages, I only see precision mathematical division in MySQL). So, for example, if I had a relation of students and courses, I might want to retrieve a list of courses in which ALL of the students are taking (perhaps, the course ID number appears under each student, or something similar). Does my question make sense? I can come up with a different query to get the job done, but it would be really nice if I could simplify it all with a simple built in function, you know?

推荐答案

没有.参见已划分我们的立场:关系部门的SQL 提供了很好的方法综述.本文以SQL Server为中心，但GROUP BY ... HAVING COUNT或double NOT EXISTS的相同2种方法仍然有效.

No there isn't. See Divided We Stand: The SQL of Relational Division for a good round up of approaches. The article is SQL Server centric but the same 2 approaches of GROUP BY ... HAVING COUNT or double NOT EXISTS still work.

对于精确的关系划分(没有余数)，GROUP_CONCAT可能会派上用场.

For exact relational division (with no remainder) GROUP_CONCAT could come in handy though.

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