[Gdal-dev] Text field size ogr2ogr PostgreSQL to MIF/MID

[Frank Warmerdam]

Mateusz Loskot wrote:
> Frank Warmerdam wrote:
>> Marc Jacquin wrote:
>>> Hi all,
>>>
>>> I am using ogr2ogr to convert a PG table into MIF/MID.
>>> The table fields are varchar(x) or char(x) type and the field width is
>>> never
>>> more than let say 50.
>>>
>>> It seems that ogr2ogr forces text fields to be 254 wide. But when you get
>>> more than 20 fields the record size exceeds the 4 K limit of MapInfo 6.
>>>
>>> Is there a PG usable type so that ogr2ogr would keep the width for
>>> exporting?
>> Marc,
>>
>> It looks like the CHARACTER(n) field type in Postgres will be treated by
>> OGR as a field with a particular width.  The code that decides whether
>> to associate a width with text fields in the driver looks like this:
> 
> Frank,
> 
> Isn't it correct assumption?
> I'm not sure I understand where is the problem here, but as I know,
> CHARACTER(n) type should be handled as fixed-width type.

Mateusz,

The problem Marc was running into is that many text field types,
like VARCHAR(n) do not end up with widths associated with them and
he wanted to know if there was a type that does.   I think CHARACTER(n)
does, which would be good.

> I may not understand rationale behind the code above well, but using
> libpq it's possible to retrieve lenght of character type from result
> set, using PQfmod() function:
> 
> //////////////////////////////////////////////////////
> const int VARCHAR_HDRSZ = 4; // usually, equal to sizeof(int)
> 
> int fmod = PQfmod(hResult, iColumnIndex);
> if (-1 != fmod)
>    length = (fmod - VARCHAR_HDRSZ);
> //////////////////////////////////////////////////////

Note that for tables we actually query various supporting tables
to get types, widths etc.  We only inspect the resultset itself for
this information from ExecuteSQL() results.

Best regards,
-- 
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