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The use of mysql sum (if ()) and count (if ()) SELECT SUM (if (category=1,size,0)), COUNT (if (category=1,true,null)) FORM tasking file; parsing sum (if (category=1,size,0))

The sum function returns a numeric value of value type, size if category=1, and 0 if category is not equal to 1.

Count (if (category=1,true,null))

The count function returns a value of Boolean type, if category=1, returns true, if category is not equal to 1, returns null, if written as count (If (category=1,1,0), all returns true, that is to say, all will be counted, while count () interruptions are true or null, count if it is not null, and do not count if it is null.

So count (if ()) should be written as count (if (expression expression, true,null)).

Mysql aggregate functions sum sum (if ()) SELECT p.Id Id, p.ImgUrl ImgUrl, p.Title Title, p.ReferOutPrice ReferOutPrice, e.`Status`, SUM (IF (e.`Status` = 1 OR e.`Status` = 2, ed.Number) according to conditions 0) FROM Product p LEFT JOIN EBOrdersDetails ed ON p.id = ed.ProductId LEFT JOIN EBOrders e ON ed.PurchaseNo = e.PurchaseNo WHERE p.StoreId = 143 AND p.`Status` >-1 GROUP BY p.Id

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