一个地方的学生和课程数量

Question

我正在尝试构建一个语句，它将为我提供三列的输出。位置，部分（该地点的部分数量）和学生（该地点的学生人数）。在我的下面的陈述中，我的子查询分别给出正确的计数;但是，当我添加我的顶级选择语句时，我将所有计数显示在学生列下，并且列出了两次位置。

SELECT DISTINCT location, student
FROM(
    SELECT location, COUNT(student_id) AS Student
    FROM section s INNER JOIN enrollment e
    ON s.section_id = e.section_id
    GROUP BY location
UNION
    SELECT location, COUNT(section_no) AS Sections
    FROM section 
    GROUP BY location
    ORDER BY location);

Answer 1

如果需要三列，则需要在SQL语句中指定它们。最简单的方法可能是COUNT(DISTINCT)：

SELECT s.location, COUNT(DISTINCT s.section_id) as NumSections,
       COUNT(student_id) AS Student
FROM section s INNER JOIN
     enrollment e
     ON s.section_id = e.section_id
GROUP BY s.location;