在 MySQL 行中添加值

Question

我有一个 table 用于存储已解析的服务器日志：

mysql> SELECT id,date,message_type FROM log_entry LIMIT 10 ;                 
+----+---------------------+--------------+
| id | date                | message_type |
+----+---------------------+--------------+
|  1 | 2015-01-08 18:13:15 |            2 |
|  2 | 2015-01-08 18:13:14 |            1 |
|  3 | 2015-01-08 18:13:12 |            1 |
|  4 | 2015-01-08 18:13:11 |            1 |
|  5 | 2015-01-08 18:13:11 |            1 |
|  6 | 2015-01-08 18:13:11 |            1 |
|  7 | 2015-01-08 18:13:10 |            1 |
|  8 | 2015-01-08 18:13:08 |            1 |
|  9 | 2015-01-08 18:13:07 |            1 |
| 10 | 2015-01-08 18:13:06 |          512 |
+----+---------------------+--------------+

每条日志按 message_type 分类。我还可以按小时对它们进行分组：

mysql> select DAY(date) as day, HOUR(date) as hour, message_type, count(message_type) FROM log_entry WHERE date >= CURDATE() - INTERVAL 2 MONTH AND message_type BETWEEN 1 AND 4 GROUP BY day,hour,message_type ORDER BY date ASC LIMIT 3;
+------+------+--------------+---------------------+
| day  | hour | message_type | count(message_type) |
+------+------+--------------+---------------------+
|    8 |   18 |            1 |                 177 |
|    8 |   18 |            2 |                  61 |
|    8 |   18 |            4 |                  14 |
+------+------+--------------+---------------------+

在此示例中，在某个日期的第 8 天和第 18 小时，我有 177 个条目，message_type 为 1，61 类型 2 和 14 类型 4.

我想每小时进行以下计算：

type(1) - type(2) - type(4)

在这种情况下 return

+------+------+--------------+---------------------+
| day  | hour | result                             |
+------+------+--------------+---------------------+
|    8 |   18 | 102                                |
+------+------+--------------+---------------------+

我这样做是因为我想在我运行的服务器上创建一个每小时 activity 显示的图表。类型 1 条目表示有人连接，类型 2 表示正常断开连接，类型 4 表示超时。

这是在数据库中做的可行的事情还是我应该在应用层做这个？

Answer 1

您可以使用 SUM() 函数和 CASE 语句来计算每个 message_type 并进行数学计算。

SELECT   DAY(date) as day, HOUR(date) as hour,  
         SUM(CASE WHEN message_type = 1 THEN 1 ELSE 0 END) -
         SUM(CASE WHEN message_type = 2 THEN 1 ELSE 0 END) -
         SUM(CASE WHEN message_type = 4 THEN 1 ELSE 0 END) as result
FROM     log_entry 
WHERE    date >= CURDATE() - INTERVAL 2 MONTH 
         AND message_type BETWEEN 1 AND 4 
GROUP BY day,hour;

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