使用LEFT加入和條件加入更有效的SELECT查詢

Question

此問題是在the back of one I asked earlier today。答案我解決了我的問題，通過限制行返回我可以看到它做我想要的。

但是現在，當我試圖運行整個查詢，沒有限制，出口到Excel分析的目的，我似乎無法得到任何地方。我在那個MySQL工作臺上啓動SQL，再次詢問我的密碼，查詢停止運行。我不確定那條信息是否會發生其他事情，以及我真正的問題是什麼：「如果可以，我怎樣才能使查詢運行得更快？」目前運行至少5分鐘，然後「踢我離開」。

當我在這裏解釋的查詢提供了什麼：

1 SIMPLE co ALL     185610 Using temporary; Using filesort 
1 SIMPLE my ref PRIMARY PRIMARY 4 bm_emails.co.id 23 
1 SIMPLE nvk eq_ref PRIMARY PRIMARY 4 bm_emails.co.id 1 

想必臨時表是造成「使用臨時」是一個問題，但我不能確定如何解決它，同時保持我的查詢。 的實際查詢是在這裏：

SELECT 
    co.email, 
    nvk.nvk_medium, 
    CAST(MIN(co.created) AS DATE) AS first_contact, 
    MIN(CASE WHEN my.my_id = 581 THEN my.data END) AS WA_Created, 
    MIN(CASE WHEN my.my_id = 3347 THEN my.data END) AS WA_Upgraded 
FROM bm_emails.cid208 co 
LEFT JOIN bm_emails.my208 my ON co.id = my.eid AND (my_id = 581 OR my_id = 3347) 
LEFT JOIN bm_emails.nvk208 nvk ON nvk.eid = co.id 
GROUP BY email 

Answer 1

如果我認爲bm_emails包含每封郵件一行，那麼這可能走得更快：

select co.email, 
     (select nvk.nvk_medium from bm_emails.nvk208 nvk where nvk.eid = co.id limit 1) as nvk_medium, 
     co.created, 
     (select min(my.data) from bm_emails.my208 my where co.id = my.eid and my.mid = 581) as WA_Created, 
     (select min(my.data) from bm_emails.my208 my where co.id = my.eid and my.mid = 3347) as WA_Updated 
from bm_emails.cid208 co; 

這可以採取以下指標的優勢：

bm_emails.nvk208(eid, nvk_medium) 
bm_emails.my208(eid, mid, data) 

當然，這取決於第一個假設，即第一個表每個電子郵件一行。

編輯：

即使有多個電子郵件地址，我仍然會嘗試這個辦法：

select cn.mail, cn.nvk_medium, cn.created, 
     (select min(my.data) from bm_emails.my208 my where co.id = my.eid and my.mid = 581) as WA_Created, 
     (select min(my.data) from bm_emails.my208 my where co.id = my.eid and my.mid = 3347) as WA_Updated 
from (select co.email, nvk.nvk_medium, min(co.created) as created 
     from bm_emails.cid208 co left join 
      bm_emails.nvk208 nvk 
      on nvk.eid = co.id 
     group by co.email, nvk.nvk_medium 
    ) cn; 

Answer 2

聯盟都往往比在連接條件使用或更快的選擇。檢查數據結果，我認爲使用UNON可能會更有意義，但必須查看數據。我也想知道更多關於whter你想看到bm_emails.cid208記錄，不會加入要麼記錄添加my_id 581或身份識別碼3347.

試試這個：

SELECT email,nvk_medium, CAST(MIN(created) AS DATE) AS first_contact,WA_Created,WA_Upgraded 
FROM 
(
    SELECT 
     co.email, 
     nvk.nvk_medium, 
     co.created AS first_contact, 
     my.data AS WA_Created, 
     NULL AS WA_Upgraded 
    FROM bm_emails.cid208 co 
    LEFT JOIN bm_emails.my208 my ON co.id = my.eid AND my_id = 581 
    LEFT JOIN bm_emails.nvk208 nvk ON nvk.eid = co.id 
    UNION ALL 
    SELECT 
     co.email, 
     nvk.nvk_medium, 
     co.created AS first_contact, 
     NULL AS WA_Created, 
     my.data AS WA_Upgraded 
    FROM bm_emails.cid208 co 
    LEFT JOIN bm_emails.my208 my ON co.id = my.eid AND my_id = 3347 
    LEFT JOIN bm_emails.nvk208 nvk ON nvk.eid = co.id 
) a 
GROUP BY email,nvk_medium,WA_Created,WA_Upgraded 

我也會考慮如果CAST（MIN（created）AS DATE）應該是Min（CAST（創建AS DATE）），取決於創建的字段的數據類型。如果是某種基於字符串的字段，那麼10/20/2014將小於2/24/2013並且將被選中。如果它存儲在日期時間類型的字段中，並且您只是簡單地關閉時間，那麼這樣做可以。