I have a USQL script and CSV extractor to load my files. However some months the files may contain 4 columns and some months they may contain 5 columns.

If I setup up my extractor with a column list for either 4 or 5 fields I get an error about the expected width of the file. Go check delimiters etc etc. No surprise.

What is the work around to this problem please given USQL is still in a newbie and missing some basic error handling?

I've tried using the **silent** clause in the extractor to ignore wider columns which is handy for 4 columns. Then getting a row count of the rowset with an IF condition that then has an extractor for 5 columns. However this leads to a world of rowset variables not being used as scalar variables in the IF expression.

Also I tried a C# style count and a sizeof(@AttemptExtractWith4Cols). Neither work.

Code snippet to give you a feel for the approach I'm taking:

```
DECLARE @SomeFilePath string = @"/MonthlyFile.csv";

@AttemptExtractWith4Cols =
    EXTRACT Col1 string,
            Col2 string,
            Col3 string,
            Col4 string
    FROM @SomeFilePath
    USING Extractors.Csv(silent : true); //can't be good.

//can't assign rowset to scalar variable!
DECLARE @RowSetCount int = (SELECT COUNT(*) FROM @AttemptExtractWith4Cols);

//tells me @AttemptExtractWith4Cols doesn't exist in the current context!
DECLARE @RowSetCount int = @AttemptExtractWith4Cols.Count();

IF (@RowSetCount == 0) THEN
    @AttemptExtractWith5Cols =
        EXTRACT Col1 string,
                Col2 string,
                Col3 string,
                Col4 string,
                Col5 string
        FROM @SomeFilePath
        USING Extractors.Csv(); //not silent
END;

//etc

```

Of course if there was such a thing as a **TRY CATCH** block in USQL this would be a lot easier.

Is this even a reasonable approach to take?

Any input would be greatly appreciated.

Thank you for your time.