I'm using MapInfo 4.5. I have two files of street centerlines. They are identical in structure. The only difference is one file is newer than the other. I'm trying to select the records in "newfile" that are not contained in "oldfile". The idea being that I could then delete all the selected records in "newfile", pack the table, and be left with just the records that did not exist in "oldfile". Using SQL Select dialog box, I select * from newfile, oldfile where newfile.obj = oldfile.obj. This produces the error message "datatype mismatch in expression". Huh? Why would this be? Before attempting this geographic comparison, I exported the underlying tables to dBase files and wrote a little program to process them based on values in a field, then open the newly created "results" file (which contains records that are in "newfile" and not in "oldfile") in MapInfo and did a SQL select where field in "results" file = field in original "newfile". Got me what I wanted, but a simple geographic comparison of the files would save a lot of steps. Can anyone explain why the SQL select where newfile.obj = oldfile.obj throws the data mismatch error? Can this not be done, or am I missing something simple here? TIA
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