SQL在MVC查询中按日期分组

Question

I am trying to make a query in my database on mvc, I want to count the purchase id and group by Order date. this is my purchase model:

public class Purchase
{
    public int PurchaseID { get; set; }
    public int CustomerID { get; set; }

    public bool DeliveryChoice { get; set; }
    public int? DriverID { get; set; }

    [DataType(DataType.Date)]
    [DisplayFormat(DataFormatString = "{0:yyyy-MM-dd}", ApplyFormatInEditMode = true)]
    [Display(Name = "Order Date")]
}

and this is my query:

SELECT  
    Purchase.PurchaseID, 
    Purchase.OrderDate,
    COUNT(*) 
From Purchase 
GROUP BY Purchase.OrderDate;

this is the message i get when i execute it:

Msg 8120, Level 16, State 1, Line 1
Column 'Purchase.PurchaseID' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

How would I fix it to allow me to group by date (yyyy-MM-dd) and count the purchaseid

Answer 1

If you need to count purchaseID groupped by date, then you need query like this one:

select 
    convert(nvarchar(10), Purchase.OrderDate, 112) as OrderDate,  
    count(Purchase.PurchaseID) 
from Purchase 
group by convert(nvarchar(10), Purchase.OrderDate, 112)

Just move Purchase.PurchaseID to the argument of aggregate function count

You're getting the error you've mentioned because when you're groupping results of query - then every selected value should be either column you're groupping by, or a result of some aggregate function - this is exactly what was stated in error text.