Question

我有一张这样的表：

// messages
+----+----------------+-----------+-------------+-------------+
| id |    content     | sender_id | receiver_id |  date_time  |
+----+----------------+-----------+-------------+-------------+
| 1  | whatever1      | 1         | 3           | 1521097240  |
| 2  | whatever2      | 3         | 1           | 1521097241  |
| 3  | whatever3      | 1         | 3           | 1521097242  |
| 4  | whatever4      | 1         | 4           | 1521097243  |
| 5  | whatever5      | 1         | 5           | 1521097244  |
| 6  | whatever6      | 5         | 1           | 1521097245  |
+----+----------------+-----------+-------------+-------------+

现在我需要计算用户sender_id = 1给不同人的消息数量。因此，假设所有这些行都在过去一天，那么结果应为3。因为sender_id = 1已向receiver_ids = 3,4,5发送了邮件。我怎么能在Mysql中做到这一点？

这是我尝试过的：

SELECT count(1) as sent_messages_num
FROM messages
WHERE sender_id = 1  
AND date_time > UNIX_TIMESTAMP(DATE_SUB(now(), INTERVAL 1 DAY))

所以我需要添加一个分组。但不确定我该怎么做？

Answer 1

尝试使用以下查询：

SELECT count(*) as sent_messages_num, receiver_id
FROM users
WHERE sender_id = 1  
AND date_time > UNIX_TIMESTAMP(DATE_SUB(now(), INTERVAL 1 DAY))
GROUP BY receiver_id

这将为您提供每个接收者的消息数量。在我再次阅读答案之后，我认为以下内容可能更适合：

SELECT count(DISTINCT receiver_id) as sent_messages_num
FROM users
WHERE sender_id = 1  
AND date_time > UNIX_TIMESTAMP(DATE_SUB(now(), INTERVAL 1 DAY))

Answer 2

您需要在distinct

中使用COUNT

SELECT count(distinct receiver_id) as sent_messages_num
FROM users
WHERE sender_id = 1  
AND date_time > UNIX_TIMESTAMP(DATE_SUB(now(), INTERVAL 1 DAY))

我如何计算每天给不同人的邮件数量？

2 个答案: