SQL GROUP BY 作为新列

Question

我正在使用 sqlite3 查询学生数据库，其中只有 students 表存在。 此处重要的列是 governorate 和 grade。

我想查看每个省超过 90% 的学生百分比，因此我编写了以下查询：

SELECT governorate, CASE
                WHEN grade > 360 AND grade <= 410 THEN '90%'
                WHEN grade > 320 THEN '80%'
                WHEN grade > 280 THEN '70%'
                WHEN grade > 240 THEN '60%'
                WHEN grade > 200 THEN '50%'
                WHEN grade > 160 THEN '40%'
                WHEN grade > 120 THEN '30%'
                WHEN grade > 80 THEN '20%'
                WHEN grade > 40 THEN '10%'
                WHEN grade > 0 THEN '0%'
                WHEN grade == 0 THEN '0'
             END AS bucket, COUNT(*) AS number FROM students GROUP BY 1, 2;

现在这只告诉您每个桶中的学生数量，而不是省学生总数的百分比。

它为每个省创建十行，我想要创建一个标记为 90-100 的新列并按该列排序。

Answer 1

在 SQLite 中，您可以使用子查询：

SELECT governorate,
       (CASE WHEN grade > 360 AND grade <= 410 THEN '90%'
                WHEN grade > 320 THEN '80%'
                WHEN grade > 280 THEN '70%'
                WHEN grade > 240 THEN '60%'
                WHEN grade > 200 THEN '50%'
                WHEN grade > 160 THEN '40%'
                WHEN grade > 120 THEN '30%'
                WHEN grade > 80 THEN '20%'
                WHEN grade > 40 THEN '10%'
                WHEN grade > 0 THEN '0%'
                WHEN grade = 0 THEN '0'
             END) AS bucket,
        COUNT(*) AS number,
        COUNT(*) * 100.0 / c.cnt as percentage
FROM students s CROSS JOIN
     (SELECT COUNT(*) as cnt FROM students) c
GROUP BY 1, 2;