左加入选择计数（*）

Question

我有一个查询，我尝试检索的行数，但在我的情况下，每次结果1下降。我想这是一个连接的问题，我不kniw如何处理这种

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

试试这个，不知道如果你使用的是MySQL或MSSQL。由于您LEFT JOIN有可能值为NULL。在MSSQL中，如果计入NULL值，结果将为NULL始终使用像COUNT这样的聚合函数。

对于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')