如何優化這個慢sql查詢？

Question

我有一個約400k行的用戶表，需要檢索其中一些（最多100），同時與其他表進行多個JOINS。 （使用mysql）

我的問題是，查詢目前有約800ms的執行時間（取46ms）。我的目標是優化查詢以減少執行時間。

我的初始查詢看起來是這樣的：

SELECT iduser, imageurl, birthdate, active, last_active, created, gender_idgender, orientation_idorientation, region_idregion, moji.moji_idmoji as moji_idmoji, status.value as status, requests.value as requestsRecv, requestssent.value as requestsSent, username.value as username, likecount.value as likeCount, reportcount.value as reportCount 
FROM user u 
    JOIN user_has_moji moji ON (u.iduser = moji.user_iduser) 
    JOIN user_has_data status ON (u.iduser = status.user_iduser AND status.datatype_iddatatype = 1) 
    JOIN user_has_data requests ON (u.iduser = requests.user_iduser AND requests.datatype_iddatatype = 3) 
    JOIN user_has_data requestssent ON (u.iduser = requestssent.user_iduser AND requestssent.datatype_iddatatype = 4) 
    JOIN user_has_data username ON (u.iduser = username.user_iduser AND username.datatype_iddatatype = 5) 
    JOIN user_has_data likecount ON (u.iduser = likecount.user_iduser AND likecount.datatype_iddatatype = 6) 
    JOIN user_has_data reportcount ON (u.iduser = reportcount.user_iduser AND reportcount.datatype_iddatatype = 7) 
WHERE banned = 0 AND active = 1 AND u.reviewstatus_idreviewstatus = 3 AND DATEDIFF(last_active,'2017-03-03 10:06:36') >=0 AND DATEDIFF(birthdate, '1999-03-03 15:06:36') >= 0 AND DATEDIFF(birthdate, '1967-03-03 15:06:36') <= 0 ORDER BY last_active DESC LIMIT 100 

我認爲原因執行時間較長的是，它有這樣做的查詢，因此我嘗試這種方法之前加入與其他表的整個用戶表：

SELECT iduser, imageurl, birthdate, active, last_active, created, gender_idgender, orientation_idorientation, region_idregion, moji.moji_idmoji as moji_idmoji, status.value as status, requests.value as requestsRecv, requestssent.value as requestsSent, username.value as username, likecount.value as likeCount, reportcount.value as reportCount 
FROM (SELECT * FROM user WHERE banned = 0 AND active = 1 AND reviewstatus_idreviewstatus = 3 AND DATEDIFF(last_active,'2017-03-03 10:01:30') >=0 AND DATEDIFF(birthdate, '1999-03-03 15:01:30') >= 0 AND DATEDIFF(birthdate, '1967-03-03 15:01:30') <= 0 ORDER BY last_active DESC LIMIT 100) as u 
    JOIN user_has_moji moji ON (u.iduser = moji.user_iduser) 
    JOIN user_has_data status ON (u.iduser = status.user_iduser AND status.datatype_iddatatype = 1) 
    JOIN user_has_data requests ON (u.iduser = requests.user_iduser AND requests.datatype_iddatatype = 3) 
    JOIN user_has_data requestssent ON (u.iduser = requestssent.user_iduser AND requestssent.datatype_iddatatype = 4) 
    JOIN user_has_data username ON (u.iduser = username.user_iduser AND username.datatype_iddatatype = 5) 
    JOIN user_has_data likecount ON (u.iduser = likecount.user_iduser AND likecount.datatype_iddatatype = 6) 
    JOIN user_has_data reportcount ON (u.iduser = reportcount.user_iduser AND reportcount.datatype_iddatatype = 7) 

想想需要連接的行數會大大減少，因此會縮短執行時間。這種改變似乎有所幫助，但查詢仍然太低。

有人可以看到執行緩慢的一些其他原因嗎？

Answer 1

你有一個非常合理的響應時間，所以你的表似乎是正確的索引。但是，讓我們看看WHERE條款（我加的是假定表的別名）：

WHERE u.banned = 0 AND u.active = 1 AND 
     u.reviewstatus_idreviewstatus = 3 AND 
     DATEDIFF(u.last_active,'2017-03-03 10:06:36') >=0 AND 
     DATEDIFF(u.birthdate, '1999-03-03 15:06:36') >= 0 AND 
     DATEDIFF(u.birthdate, '1967-03-03 15:06:36') <= 0 

首先，刪除datediff()並做簡單的比較。我想你想要這樣的：

WHERE u.banned = 0 AND u.active = 1 AND 
     u.reviewstatus_idreviewstatus = 3 AND 
     u.last_active >= '2017-03-03 10:06:36' AND 
     u.birthdate >= '1999-03-03 15:06:36' AND 
     u.birthdate <= '1967-03-03 15:06:36' 

我有點懷疑，最後的三個條件，但使用datediff()是混亂的。這是簡單比較更好的原因之一。

您需要快速找到這些行，這表明兩個指標之一：

users(banned, active, reviewstatus_idreviewstatus, last_active, birthdate) 

或

users(banned, active, reviewstatus_idreviewstatus, birthdate, last_active) 

這取決於其whittles下來的數據更多。我的猜測是last_active更重要。還要注意，前三個鍵可以按任意順序排列，只要它們是前三個。

這可能有幫助，但我懷疑你會看到一個驚人的進步。