使MySQL查詢選擇通過聲明

與組的最高時間戳這是我的查詢：使MySQL查詢選擇通過聲明

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，現在看起來是這樣的：

但我想唯一選擇包含字段log_timestamp的最大值的行。（在這種情況下2017-08-15 06:09:52）。我試圖用類似的東西：

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

，但它不喜歡的工作：

HAVING transactions.log_timestamp >= max(log_timestamp);

我到底做錯了什麼？

來源

2017-08-28 CMDR Nimmerzeth

這裏是另一種解決方案。如果您只希望在選擇列表的所有列中爲每個不同值創建一行，則不需要GROUP BY。你可以做同樣的事情SELECT DISTINCT如下：

SELECT DISTINCT 
    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 
ORDER BY log_timestamp DESC 
LIMIT 1

既然你只是想最大log_timestamp行，你可以通過柱降下來，使用極限排序，結果中只返回第一行。

來源

2017-08-28 15:12:49

什麼是最適合大桌子上的性能？ –

性能最好的方法是使用索引優化表。您沒有爲您的表發佈「SHOW CREATE TABLE」，也不知道「log_timestamp」屬於哪個表，因此我無法評論哪些索引是需要的。 –

你可以嘗試一個子查詢，像

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

來源

2017-08-28 13:05:51 Sebastian

有語法錯誤，在HAVING部分使用這個子查詢工作，並加入當然內部連接=） –

Thx幫助，塞巴斯蒂安 –

使MySQL查詢選擇通過聲明

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