mysql - 选择带有左连接的 count(*)

Question

我有一个查询，我尝试检索行数，但在我的情况下，每次都会删除结果 1。我想这是一个连接问题，我不知道如何处理这个问题

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

尝试一下，不确定您使用的是MySQL还是MSSQL。由于您LEFT JOIN，值有可能是NULL。在 MSSQL 中，如果考虑 NULL 值，则结果将为 NULL 在使用 COUNT 等聚合函数时始终如此>。

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')