Alias variable in MapBasic

Question

I'm having a bit of trouble with the Alias variable in MapBasic. In short, I have a table where I was to group by a specific column. Then I want to run through each unique value from the grouped table through the original one and combine each one. So I have a table of cities with a column of which country each city is in. My program gives the user to choose a table and a column within that table to gorup by. Then it basically goes like this:

Dim aSelection, aGrouped as Alias 
Selection = selectedTable & "." & selectedColumn
Select * from selectedTable into Temp_GroupedTable Group By selectedColumn
aGrouped = Temp_GroupedTable & "." & selectedColumn

So a) is this code correct? b) How can I fetch the data from each row in the Temp_GroupedTable so that I can compare it with the values in the original table? I currently have this general setup within a loop:

Fetch rec i from Temp_GroupedTable
Select * from selectedTable into New_Temp_TAB Where aSelection = aGrouped
Objects Combine

I know there is something wrong... But I don't know how to fix it. Any ideas?

Answer 1

Try this:

Dim aSelection, aGrouped as Alias
Dim sGrouped As String
aSelection = selectedTable & "." & selectedColumn
Select * from selectedTable 
 into Temp_GroupedTable 
 Group By aSelection
aGrouped = "Temp_GroupedTable." & selectedColumn
Fetch First from Temp_GroupedTable
Do Until EOT(Temp_GroupedTable)
 aGrouped = sGrouped
 Select * from selectedTable 
 into New_Temp_TAB 
 Where aSelection = sGrouped
‘** Objects Combine ...
 Fetch First from Temp_GroupedTable
Loop

I changed your first selection a bit and also the assignment of the aGrouped alias variable. And then I made some changes to your loop. I’m not entirely sure what more you want to do within the loop.

I’m not entirely sure about this line: Where aSelection = aGrouped

You might need to read the value into a string or numeric value first. But give it a go and let us know

• KDawg: Thanks @peter. But for some reason I get an error message "Variable or Field Temp_GroupedTable.Region not defined" for the line of code you weren't sure about. I can assure you however that the column does exist. Any ideas on solving this?
• Peter Horsbøll Møller: Yeah, that was what I thought. I have modified the code a bit to get around that issue. Notice that I'm assuming your column is a Char() column in my example

Answer 2

Thanks for the help @Peter! I ended up using the following code which did what I needed:

Sub Process
Dim aGrouped as Alias
Print "Object Combiner Loaded!"
Select * from selectedTable into Temp_GroupedTable Group By selectedColumn
Print "Grouping Successful"
'*** Groups by user selected column
aSelection = selectedTable & "." & selectedColumn
Select * from selectedTable 
 into Temp_GroupedTable 
 Group By aSelection
aGrouped = "Temp_GroupedTable." & selectedColumn
Fetch First from Temp_GroupedTable '*** Fetchs first row from grouped table
'*** Runs through table to combine objects by each individual value
Do Until EOT(Temp_GroupedTable)
 sGrouped = aGrouped
 Select * from selectedTable 
 Where aSelection = sGrouped
 Objects Combine Data selectedColumn = sGrouped 'Retains value of 
 'selected column
 Fetch Next from Temp_GroupedTable
Loop
End Sub