Question

我有stockcards和stockcategories表。

我想显示类别并显示在此类别下打开多少个证券卡。

SELECT a.stockCatID, a.stockCatName, f.nProductsInside 
FROM stockcategories a 
LEFT JOIN 
        (
            SELECT COUNT(b.stockID) AS nProductsInside 
            FROM stockcards b 
        ) 
        f ON a.stockCatID = f.stockCatID

好吧它返回#1054 - Unknown column 'f.stockCatID' in 'on clause'显然我犯了错误..

Answer 1

尝试使用类似的东西：

SELECT a.stockCatID, a.stockCatName, COUNT(b.stockID) AS nProductsInside
FROM stockcategories a 
LEFT JOIN stockcards b ON a.stockCatID = b.stockCatID
GROUP BY a.id

其中a.id是stockcategories表

中的主键

Answer 2

SELECT a.stockCatID, a.stockCatName, COUNT(b.stockID) as nProductsInside 
FROM stockcategories a 
LEFT JOIN stockcards b ON a.stockCatID = b.stockCatID 
group by a.stockCatID

你也可以这样做（未经验证）你要坚持你的查询

SELECT a.stockCatID, a.stockCatName, f.nProductsInside 
FROM stockcategories a 
LEFT JOIN 
(
    SELECT COUNT(b.stockID) AS nProductsInside, stockCatID
    FROM stockcards b 
) 
f ON a.stockCatID = f.stockCatID

Answer 3

f是SELECT COUNT（b.stockID）结果的别名...... 所以f没有collumn

查询从不同的表中计算父类别下的项目

3 个答案: