左加入選擇計數（*）

Question

我有一個查詢，我嘗試檢索的行數，但在我的情況下，每次結果1下降。我想這是一個連接的問題，我不kniw如何處理這種

SELECT 
    COUNT(*) AS summe 
FROM 
    feeds 
    LEFT JOIN cat_product cp 
    ON cp.product_id = feeds.productid 
WHERE 1 = 1 
    AND cp.price BETWEEN 950 
    AND 1450 
    AND cp.ram_cap BETWEEN 5 
    AND 11 
    AND feeds.tdcategoryname LIKE '%Laptop%' 
    AND feeds.brand IN ('Dell', 'Lenovo', 'Acer', 'Asus') 
GROUP BY cp.product_id 

Answer 1

試試這個，不知道如果你使用的是MySQL或MSSQL。由於您LEFT JOIN有可能值爲NULL。在MSSQL中，如果計入NULL值，結果將爲NULL始終使用像COUNT這樣的聚合函數。

對於MySQL

SELECT 
    COUNT(IFNULL(cp.Procuct_id,0)) AS summe 
FROM 
    feeds 
    LEFT JOIN cat_product cp 
    ON cp.product_id = feeds.productid 
WHERE 1 = 1 
    AND cp.price BETWEEN 950 
    AND 1450 
    AND cp.ram_cap BETWEEN 5 
    AND 11 
    AND feeds.tdcategoryname LIKE '%Laptop%' 
    AND feeds.brand IN ('Dell', 'Lenovo', 'Acer', 'Asus')