On 2002.11.18 19:34:10 -0500 Blas Rodriguez Somoza wrote:

> Hello David
>
> There are two problems in the mapping.
>
> The first problem is that the typeInfo serves to map SQL types to
> java.sql.Types, and can be many to one but not one to many.
> Each SQL type must have a row in the table and only one.

Is this in the spec?

In the case of

> BLOB subtype, the solution I choose was to specify the
> subtype as part of the SQL name, thus there are only one line for each
> type because there are not generic BLOB in typeInfo.
>
> But there is another clearer argument . There is a condition that
> must be meet to map a SQL type to a java type. The SQL type
> must be able to store values from the min to the max of the java type,
> and if the type is an exact one, integers and
> decimal/numeric, then the values must not loose precision.
>
> For instance, for Integer the values must be between
> 2^31-1(2.147.483.647) and -2^31 (2.147.483.648) which are exactly the
> limits is interbase, so the integer type in interbase can be mapped to
> java.sql.Types.INTEGER.
>
> For BIGINT(equivalent to Long) this means that the field must allow
> values from 2^63-1 to -2^63 without loosing of precision,
> what is not true for NUMERIC(18,0). So NUMERIC(18,0) can't be mapped to
> BIGINT because it can't containt values between the max and
> min of a BIGINT without loosing precision, and the tests with setLong on
> this field will fail because the value get will be
> different from the one set.
>
> So the mapping NUMERIC(18,0) to BIGINT is an illegal one and must be
> removed until firebird have a INT64 field.

I looked in my sql reference, and apparently I made a mistake, confusing
NUMERIC and DECIMAL. NUMERIC requires exact precision, DECIMAL allows
greater precision than that requested. I haven't checked yet to verify
that Long.MAX_VALUE can be stored in DECIMAL(18.0) but it is at least
allowed by the sql spec.

>
> Reviewing this change, I see you remove the type "BLOB SUBTYPE > 1" I
> don't know exactly why, but I suppose is a mistake.

I'll look into this shortly.

thanks
david jencks

>
> Regards
> Blas Rodriguez Somoza
>
> ----- Original Message -----
> From: "David Jencks" <davidjencks@...>
> To: <Firebird-Java@yahoogroups.com>
> Sent: Monday, November 18, 2002 8:07 PM
> Subject: Re: [Firebird-Java] Re: Only real types in
> FBDatabaseMetaData.getTypeInfo
>
>
> > When I looked at this and implemented the BIGINT support, I didnt see
> > anything in the spec or javadocs that indicated that the Type returned
> from
> > a column should be the same as that used to get the sql to create the
> > column. In other words, I think the Type to db-specific sql types can
> be
> > many to one. Do you have some evidence that the spec authors intend
> > otherwise? I don't remember too clearly but I thought there were some
> > hints that the relation between Type and db-specific sql type could be
> > many-many.
> >
> > I would think a more generally plausible algorithm for you would be to
> > compare the db specific sql for the Type from the column and the Type
> from
> > typeinfo and decide if they are compatible.
> >
> > does your algorithm work for any other databases?
> >
> > thanks
> > david jencks
> >
> > On 2002.11.18 12:05:17 -0500 sp64_asaon wrote:
> > > --- In Firebird-Java@y..., David Jencks <davidjencks@d...> wrote:
> > > > Can you please explain the problem you are having in considerably
> > > more
> > > > detail?
> > >
> > > I would like to explain it on the hand of a pseudo code extraction:
> > >
> > > // Returns database specific info about the given data type.
> > > MyTypeInfo MyMetaData.getTypeInfo(int type);
> > >
> > > // Returns info about the most matching data type
> > > // supported by the underlying database
> > > MyTypeInfo MyMetaData.getSupportedType(int type) {
> > > MyTypeInfo ti = null;
> > > switch (type) {
> > > ...
> > > case Types.BIGINT:
> > > if ((ti = getTypeInfo(Types.BIGINT) == null)
> > > if ((ti = getTypeInfo(Types.DOUBLE) == null)
> > > ti = getTypeInfo(Types.INTEGER);
> > > break;
> > > ...
> > > }
> > > return ti;
> > > }
> > >
> > >
> > > // Update-Strategy:
> > >
> > > columnType = X; // retrieved from getColumnns
> > > desiredType = Types.BIGINT;
> > > supportedType = myMetaData.getSupportedType(desiredType);
> > >
> > > boolean haveToUpdate = columnType != supportedType
> > > // and other criteria depending on the data type:
> > > // || columnSize < neededSize
> > > // || ...
> > >
> > >
> > > Example with your changes:
> > > columnType = Types.NUMERIC;
> > > desiredType = Types.BIGINT;
> > > supportedType = Types.BIGINT;
> > > haveToUpdate = true;
> > > // columnType will never match the 'erroneosly'
> > > // reported supported type ==> repeated updates
> > >
> > > Example without your type entry for BIGINT:
> > > columnType = Types.DOUBLE;
> > > desiredType = Types.BIGINT;
> > > supportedType = Types.DOUBLE;
> > > haveToUpdate = false;
> > > // columnType matches the mapped supported type
> > >
> > >
> > > Best regards
> > > Stephan
> > >
> > >
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