[erlang-questions] Issue using variable length fields with Erlang ODBC

[Ben Murphy]

I think the problem is here:

https://github.com/erlang/otp/blob/maint/lib/odbc/c_src/odbcserver.c#L1308

MAXCOLSIZE = 8001

I observed this appearing as truncation for large return results but I
guess it is possible it allocates 8001 and tries to dump you back
9000. But ODBC driver has a lot of strange behaviour and I would avoid
using it if possible.

On Mon, Apr 11, 2016 at 1:58 PM, Rob A'Court <rob@REDACTED> wrote:
> When querying variable length fields using ODBC in Erlang, the response
> returned seems to be gibberish.
>
>
>
> We can query tables in a MS SQL Server database but if the table contains a
> VarCharMax or NVarCharMax field (both variable length) then the result
> returned is not what we expect. For NVarCharMax a binary is returned which
> has part of the original query and other seemingly random data as if it’s
> the wrong area of memory. For VarCharMax an empty list is always returned.
>
>
>
> In our particular scenario we are trying to get a ShowPlanXML from MS SQL
> Server which comes back as a NVarCharMax and there is no way of converting
> it to a fixed length field type to work around the issue.
>
>
>
> The issue does not seem to be with the ODBC driver as trying the same thing
> in python works fine.
>
>
>
> Here is what we are trying to do in Elixir:
>
>
>
> :odbc.start
>
> {:ok, connection} = :odbc.connect('Driver={ODBC Driver 11 for SQL Server};
> Server=TheServer;Uid=sa;Pwd=password;Database=TheDatabase',[])
>
> IO.inspect :odbc.sql_query(connection, 'set showplan_xml on')
>
> IO.inspect :odbc.sql_query(connection, 'Select * from customers'), limit:
> 9000
>
>
>
>
>
> Here is the equivalent in python that works fine:
>
>
>
> #!/usr/bin/env python
>
> import pyodbc
>
> conn = pyodbc.connect('Driver={ODBC Driver 11 for SQL Server};
> Server=TheServer;Uid=sa;Pwd=password;Database=TheDatabase')
>
> cur = conn.cursor()
>
> cur.execute('set showplan_xml on')
>
> cur.execute('Select * from customers')
>
>
>
> for row in cur :
>
>   print row
>
>
>
>
>
> Many thanks!
>
>
>
> Rob
>
>
>
>
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