Go Premium for a chance to win a PS4. Enter to Win

x
?
Solved

Retrieving the MAX Value from a SQL Column?

Posted on 2014-02-27
5
Medium Priority
?
385 Views
Last Modified: 2014-02-27
I am trying to retrieve a MAX value from a column in a table. The issue is if the table contains NO records...I get an error saying:

"Conversion from type 'DBNULL' to type 'Integer' is not valid"

I understand why I get the error because it's returning a NULL value. I'm just not sure how to structure the statement. I know how to return a MAX value in a populated table, just not in an empty table.

    Public Function GetMaxID(ByVal tbl As String, ByVal keyFld As String, ByRef EH As ErrorHandling.ErrorHandler)
        Try
            DBConnection(EH)

            If EH.Bool Then
                sSQL = "SELECT MAX(ISNULL(" & keyFld & ",0)) + 1 FROM " & tbl
                cmd = New SqlCommand(sSQL, cnn)
                EH.Number = cmd.ExecuteScalar()
            End If

        Catch ex As Exception
            EH.ErrorMessage = "GetMaxID() - " & ex.Message & "...Contact Engineering!" & "~E"
        Finally
            cnn.Dispose()
        End Try

        Return EH
    End Function

Open in new window

0
Comment
Question by:BlakeMcKenna
  • 2
  • 2
5 Comments
 
LVL 66

Expert Comment

by:Jim Horn
ID: 39892134
>ByVal keyFld As String
>MAX(ISNULL(" & keyFld & ",0))
The problem you're having here is that you're trying to do a MAX() on a character data type, which means anything other than numbers (NULL, 'banana', '1st place') is going to throw an error, if not during the MAX then definately during the + 1.

I recommend two things.
Change keyFld to ISNULL(keyFld, 0) to convert NULLs to zeros
Filter out these values by adding this to your query
WHERE ISNUMERIC(keyFld) = 1
0
 
LVL 143

Accepted Solution

by:
Guy Hengel [angelIII / a3] earned 2000 total points
ID: 39892145
move the IsNull to outside the MAX function, and it should work ...
 sSQL = "SELECT ISNULL ( MAX( " & keyFld & ",0)) + 1 FROM " & tbl
0
 

Author Comment

by:BlakeMcKenna
ID: 39892159
Here is the new statement and it doesn't return anything!

Select ISNULL(ID,0) As MaxValue
  From [Temp]
 Where ISNUMERIC(ID) = 1

Open in new window

0
 

Author Closing Comment

by:BlakeMcKenna
ID: 39892168
Thanks Guy...that worked!
0
 
LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 39894109
please show the output of this query:
Select id, ISNUMERIC(ID) 
  From [Temp] 

Open in new window


rereading the question, I think you are anyhow heading into a wrong direction.
it looks like you want to use a "IDENTITY" field instead of doing this yourself ...
http://technet.microsoft.com/en-us/library/aa933196%28v=sql.80%29.aspx
0

Featured Post

NFR key for Veeam Agent for Linux

Veeam is happy to provide a free NFR license for one year.  It allows for the non‑production use and valid for five workstations and two servers. Veeam Agent for Linux is a simple backup tool for your Linux installations, both on‑premises and in the public cloud.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Audit has been really one of the more interesting, most useful, yet difficult to maintain topics in the history of SQL Server. In earlier versions of SQL people had very few options for auditing in SQL Server. It typically meant using SQL Trace …
In this article I will describe the Copy Database Wizard method as one possible migration process and I will add the extra tasks needed for an upgrade when and where is applied so it will cover all.
Loops Section Overview
Look below the covers at a subform control , and the form that is inside it. Explore properties and see how easy it is to aggregate, get statistics, and synchronize results for your data. A Microsoft Access subform is used to show relevant calcul…

824 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question