Question

I am trying to use a CAST() in an SQL statement but it doesn’t allow me to see the CAST(myDateTime, Date) as myLoginShortDate in the group by? I only know the basics of SQL and I am trying to learn more.
May data looks like this:

CustomerID int, null
Email varchar(60)
DateEntered DateTime

I am trying to get the a grouping by the date part of the datetime and grouped on the Email

My stored procedure select part looks like this:

       select  cll.Email,CAST(cll.DateEntered as Date) as LoginDate, 
              COUNT(cll.email) as FailedCount
            from [GC].[dbo].[CustomerLoginLog] as cll
            where [CustomerId] is null
            group by LoginDate, cll.Email
            order by FailedCount desc`

It is returning "Invalid column name ‘LoginDate’"

I want to be able to see:

Email, LoginDate, FailedCount

[e-mail], 11/01/12, 21

[e-mail], 11/01/12, 17

[e-mail], 10/30/12, 15

and so on. I am sure this is just a beginners mistake. I have this post all messed up but I hope somebody understands it. The select format looks better on my computer.

Answer 1

The GROUP BY statement is evaluated before the SELECT statement, so SQL server doesn’t know about the alias you gave the expression in the SELECT statement. To remedy this, you simply have to repeat the expression in the GROUP BY:

GROUP BY CAST(cll.DateEntered AS Date)

Or wrap the simple part of your query with a CTE, and do the grouping on the CTE results:

;WITH MyQuery AS 
(
    SELECT
        cll.Email
        ,CAST(cll.DateEntered AS Date) AS LoginDate
    FROM 
        [GC].[dbo].[CustomerLoginLog] AS cll
    WHERE 
        cll.[CustomerId] IS NULL
)
SELECT 
    Email
    ,LoginDate
    ,COUNT(*) AS FailedCount
FROM 
    MyQuery
GROUP BY 
    LoginDate, Email
ORDER BY 
    FailedCount DESC

Alternatively you could include the content of the CTE as in a nested SELECT statement as Mahmoud pointed out.