mysql - 使 MySQL 查询使用 group by 语句选择最大时间戳

Question

这是我的查询:

SELECT 
    log_timestamp, 
    system_name,
    faction_name,
    faction_allegiance, 
    faction_government_type, 
    current_state, 
    pending_state,
    recovering_state,
    influence AS influence,
    transactions.transaction_id
FROM `bgs`.`faction_log`
    INNER JOIN `factions` ON `factions`.`faction_id` = `faction_log`.`faction_id`
    INNER JOIN `transactions` ON `transactions`.`transaction_id` = `faction_log`.`transaction_id`
    INNER JOIN `system_log` ON `system_log`.`transaction_id` = `transactions`.`transaction_id`
    INNER JOIN `systems` ON `systems`.`system_id` = `transactions`.`associated_system_id` 
WHERE
    log_timestamp BETWEEN bgs.find_closest_tick_time(date('2017-08-14')) AND bgs.find_closest_tick_time(DATE_ADD(date('2017-08-14'), INTERVAL 1 DAY)) AND
    associated_system_id = 4 
GROUP BY 
    faction_name,
    log_timestamp,
    system_name,
    faction_allegiance, 
    faction_government_type, 
    current_state, 
    pending_state,
    recovering_state,
    influence,
    transactions.transaction_id

它工作正常，现在看起来像这样:

+--------------------+------------+------ ----------+
|日志时间戳 |系统名称 |派系名称 |
+--------------------+------------+------------ -----+
| 2017-08-14 11:18:46 |凪井 | Nagii专制|
| 2017-08-14 12:38:03 |凪井 | Nagii专制|
| 2017-08-14 13:40:18 |凪井 | Nagii专制|
| 2017-08-15 06:09:52 |凪井 | Nagii专制|
| 2017-08-14 11:18:46 |凪井 |凪井网络 |
| 2017-08-14 12:38:03 |凪井 |凪井网络 |
| 2017-08-14 13:40:18 |凪井 |凪井网络 |
| 2017-08-15 06:09:52 |凪井 |凪井网络 |
| 2017-08-14 11:18:46 |凪井 |凪井队 |
| 2017-08-14 12:38:03 |凪井 |凪井队 |
| 2017-08-14 13:40:18 |凪井 |凪井队 |
| 2017-08-15 06:09:52 |凪井 |凪井队 |
| 2017-08-14 11:18:46 |凪井 |凪井联盟 |
| 2017-08-14 12:38:03 |凪井 |凪井联盟 |
| 2017-08-14 13:40:18 |凪井 |凪井联盟 |
| 2017-08-15 06:09:52 |凪井 |凪井联盟 |
| 2017-08-14 11:18:46 |凪井 | Nagii联合公司 |
| 2017-08-14 12:38:03 |凪井 | Nagii联合公司 |
| 2017-08-14 13:40:18 |凪井 | Nagii联合公司 |
| 2017-08-15 06:09:52 |凪井 | Nagii联合公司 |
+--------------------+------------+------------ -----+
一组 20 行(0.00 秒)


但我只想选择包含字段 log_timestamp 最大值的行。 (在本例中为 2017-08-15 06:09:52)。我尝试使用类似的东西:

HAVING transactions.log_timestamp >= max(date('2017-08-15 06:09:52'));

但它不是那样工作的:

HAVING transactions.log_timestamp >= max(log_timestamp);

我做错了什么？

Answer 1

你可以试试子查询，比如

WHERE
    log_timestamp = (
      SELECT MAX(log_timestamp) 
      FROM `bgs`.`faction_log`
      WHERE log_timestamp BETWEEN bgs.find_closest_tick_time(date('2017-08-14')) AND bgs.find_closest_tick_time(DATE_ADD(date('2017-08-14'), INTERVAL 1 DAY)) AND associated_system_id = 4
) AND associated_system_id = 4