Useing variables in a select statement

[James Harvie]

Hello All,

 

I am a veterane user of MI Pro but very new to developing MB programs, I hope you can help on this.  I am wanting to read from a configuration file (.TXT) file the "Where" components of a Select statement into a variable and then run the Select statement using the variable name.  So for example, the statement …

 

Select * from Landuse where CATEGORY=”MIXED” into TT2

 

.. would read in MB code as the following.

            Select * from Landuse where XX into TT2

 

I have no trouble reading the "Where" part of the select statement  into a variable as CATEGORY=”MIXED” but when I run the program, all records in the Landuse table are being selected not just the ones that are classified as Mixed.  Can you help with what I am doing wrong.

 

Thanks in advance

Jamie

 

 

[Thomas Bacon]

Hi Jamie,

 

You are nearly there. You need to build up the sql command as a string and then execute the string with run command. At the moment, MapInfo would interpret your sql as:

 

Select * from Landuse where "CATEGORY=""MIXED""" into TT2

 

This is interpreted by MapInfo as being true for all records. I’m not entirely sure why, but I assume it is because you are not comparing a field to anything but simply inserting a string into the where condition.

 

By building up the command as a string first, you can avoid this problem. This method essentially ‘hard-codes’ the string from XX into the command string which you can then run using the Run Command statement:

 

Dim sCmd as String

 

sCmd = "Select * from Landuse where " & XX & " Into TT2"

Run Command sCmd

 

Hope this helps,

 

Tom Bacon

GIS Engineer, Mouchel

T 01444 472380 │ E thomas...@mouchel.com │ W www.mouchel.com

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[James Harvie]

Thanks Tom,

 

I bet this will do the trick

 

Jamie

[Craig Slawson]

Further to Toms explanation you might find problems using double quotes in both the variable and in the Select Statement - try using single quotes for one of them if it doesn't work, if I have to include double quotes, then I usually set them up as a function, but this would require your 'CATEGORY=”MIXED”' to be two variables of 'CATEGORY' and 'MIXED' which might mean a complete rewriting of your routine, please come back to me if you need this explaining more clearly!

Craig

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