Question

我有一个从数据库返回计数的查询。查询的示例输出：

查询：

SELECT COUNT(*)
FROM `submissions`
INNER JOIN `events`
ON `submissions`.event_id = `events`.id
WHERE events.user_id IN (
SELECT id
FROM `users`
WHERE users.created_at IS NOT NULL
GROUP BY `events`.id

有没有办法轻松获取输出并将其拆分为预定义的值范围（0-100,101-200等），表明属于特定范围的行数？

Answer 1

在select子句中使用case表达式。

SELECT `events`.id , 
case when COUNT(`events`.id) between 0 and 100 then '0 - 100'
when COUNT(`events`.id) between 100 and 200 then '100 - 200'
end as Range
FROM `submissions`
INNER JOIN `events`
ON `submissions`.event_id = `events`.id
WHERE events.user_id IN (
SELECT id
FROM `users`
WHERE users.created_at IS NOT NULL
GROUP BY `events`.id

Answer 2

通过利用SUM()聚合来使用条件计数。

如果您需要列中的范围

SELECT SUM(CASE WHEN n BETWEEN(  0 AND 100) THEN 1 ELSE 0 END) '0-100',
       SUM(CASE WHEN n BETWEEN(101 AND 200) THEN 1 ELSE 0 END) '101-200'
       -- , add other ranges here
  FROM (
      SELECT COUNT(*) n
        FROM submissions s JOIN events e
          ON s.event_id = e.id JOIN users u
          ON e.user_id = u.id
       WHERE u.created_at IS NOT NULL
       GROUP BY e.id
  ) q

示例输出

+-------+---------+
| 0-100 | 101-200 |
+-------+---------+
|     2 |       3 |
+-------+---------+
1 row in set (0.01 sec)

如果你想把它作为一套你可以做到

SELECT CONCAT(r.min, '-', r.max) `range`,
       SUM(n BETWEEN r.min AND r.max) count
  FROM (
      SELECT COUNT(*) n
        FROM submissions s JOIN events e
          ON s.event_id = e.id JOIN users u
          ON e.user_id = u.id
       WHERE u.created_at IS NOT NULL
       GROUP BY e.id
  ) q CROSS JOIN (
      SELECT 0 min, 100 max
      UNION ALL
      SELECT 101, 200
      -- add other ranges here
  ) r
 GROUP BY r.min, r.max

示例输出

+---------+-------+
| range   | count |
+---------+-------+
| 0-100   |     2 |
| 101-200 |     3 |
+---------+-------+
2 rows in set (0.01 sec)

将数据分组到范围中

2 个答案: