[英]MySQL Query extremely slow
以下查詢花費太多時間(此刻為0.8169sec)來顯示20個條目,但我找不到原因...
SELECT
`Order`.ID,
Order_Type.Description as OrderTypeDescription,
`Order`.OrderType as OrderType,
DATE_FORMAT(`Order`.InsertDate, '%d.%m.%Y') as OrderInsertDate,
round(sum(Item_Price.Amount),2) as OrderAmount,
c1.ID as buyerCustomerId,
c2.ID as sellerCustomerId,
c1.CompanyName as BuyerCompany,
c2.CompanyName as SellerCompany,
c1.ID as BuyerCustomer,
c2.ID as SellerCustomer
FROM `Order`
INNER JOIN Order_Type ON Order_Type.ID=`Order`.OrderType
INNER JOIN Customer as c1 ON c1.ID=`Order`.BuyerCustomer
INNER JOIN Customer as c2 ON c2.ID=`Order`.SellerCustomer
INNER JOIN Item ON Item.`Order`=`Order`.ID
INNER JOIN Item_Price ON Item_Price.Item=Item.ID
GROUP BY `Order`.ID,OrderType,OrderTypeDescription,buyerCustomerId,sellerCustomerId,BuyerCustomer,SellerCustomer
ORDER BY `Order`.ID DESC
LIMIT 20
EXPLAIN顯示以下輸出: http : //pastebin.com/5f9QYizq
我並不是非常擅長優化查詢,但是我認為性能不佳的原因可能是項目和item_price表上的聯接(和總和),因為兩個表中都有很多行(項目:16974, item_price:23981),因為每個項目都有一個或多個item_prices,它們總計為訂單金額。
任何想法如何使此查詢更快?
您可以嘗試使用相關子查詢,而不要使用group by
:
SELECT o.ID, ot.Description as OrderTypeDescription, ot.OrderType as OrderType,
DATE_FORMAT(o.InsertDate, '%d.%m.%Y') as OrderInsertDate,
(SELECT round(sum(ip.Amount), 2)
FROM Item i INNER JOIN
Item_Price ip
ON ip.Item = i.ID
WHERE i.`Order` = o.ID
) as OrderAmount,
c1.ID as buyerCustomerId,
c2.ID as sellerCustomerId,
c1.CompanyName as BuyerCompany,
c2.CompanyName as SellerCompany,
c1.ID as BuyerCustomer,
c2.ID as SellerCustomer
FROM `Order` o INNER JOIN
Order_Type ot
ON ot.ID = o.OrderType INNER JOIN
Customer c1
ON c1.ID = o.BuyerCustomer INNER JOIN
Customer c2
ON c2.ID = `Order`.SellerCustomer
ORDER BY o.ID DESC
LIMIT 20;
這樣可以節省GROUP BY
開銷。
您甚至可以將LIMIT
移至子查詢,假設聯接未過濾任何行:
SELECT o.ID, ot.Description as OrderTypeDescription, ot.OrderType as OrderType,
DATE_FORMAT(o.InsertDate, '%d.%m.%Y') as OrderInsertDate,
(SELECT round(sum(ip.Amount), 2)
FROM Item i INNER JOIN
Item_Price ip
ON ip.Item = i.ID
WHERE i.`Order` = o.ID
) as OrderAmount,
c1.ID as buyerCustomerId,
c2.ID as sellerCustomerId,
c1.CompanyName as BuyerCompany,
c2.CompanyName as SellerCompany,
c1.ID as BuyerCustomer,
c2.ID as SellerCustomer
FROM (SELECT o.*
FROM `Order` o
ORDER BY o.id DESC
) o INNER JOIN
Order_Type ot
ON ot.ID = o.OrderType INNER JOIN
Customer c1
ON c1.ID = o.BuyerCustomer INNER JOIN
Customer c2
ON c2.ID = `Order`.SellerCustomer
ORDER BY o.ID DESC
LIMIT 20;
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