在SQL Server 2012

Question

我想从count函数计算结果集的平均值。我使用了这个查询：

SELECT 
    CAST(AVG(purchase) AS NUMERIC (5,3))
FROM 
    (SELECT count(*) as purchase 
     FROM transactions
     GROUP BY payer_id) X

但我得到的结果是＆＃34; 1＆＃34;。我使用Excel来验证这个结果，它应该是1,635264484。

我还想返回count（）列表和此列表的平均值，因此我重写了我的查询：

SELECT 
    tr1.payer_id, count(*) AS purchase
FROM 
    transactions AS tr1
GROUP BY 
    payer_id 

UNION ALL 

SELECT 'avg = ', AVG(X.purchase) 
FROM 
    (SELECT count(*) as purchase
     FROM transactions tr2
     GROUP BY tr2.payer_id) X

现在，查询运行一段时间，然后显示以下错误消息：

  

将数据类型varchar转换为数字时出错。

列payer_id是数字（38,0）。

有什么想法吗？

Answer 1

您无法将'avg ='转换为由于您的UNION而尝试的数字，因为您的player_id是数字。

如果你将payer_id转换为文本，它应该有效：

SELECT 
    CAST(tr1.payer_id AS VARCHAR(255)), count(*) AS purchase
FROM 
    transactions AS tr1
GROUP BY 
    payer_id 

UNION ALL 

SELECT 'avg = ', AVG(X.purchase) 
FROM 
    (SELECT count(*) as purchase
     FROM transactions tr2
     GROUP BY tr2.payer_id) X