"null" values in Query result format about archived-sansa-query HOT 4 CLOSED

Hi @purohitsumit ,
many thanks for the issue. Indeed, this is related to the variable binding as described on issue #13 and the null values are because of the result set containing all the schema (including RDF terms).

We will try to resolve this issue as soon as possible and map the bindings to the variables present in the projection clause.

Best regards,

from archived-sansa-query.

This is actually a design issue of .sparql() that it exposes the raw SQL result set - without the mapping that creates the actual bindings having been applied. So NULL values are valid at this stage.
RDF terms of different datatypes in general need to be represented with different and/or multiple SQL columns if only using standard SQL datatypes; "RDFTerm" is typically NOT a datatype supported by SQL.
For example: If in SPARQL there are two bindings with a string and an int value for ?x, in the SQL result set there will conceptually be an x_int and an x_string column. The two rows will have one column holding the value and the other one set to NULL.

Note: Improving the naming of columns is subject of #13.

from archived-sansa-query.

@GezimSejdiu @dgraux This is an API design issue and we discussed some time ago, that we will face the same issue with ontop - i.e. any sparql-to-sql rewrite has at least two parts: the SQL result table and the mapping to SPARQL bindings.
I see the following options that .sparql() return for SELECT queries:

• Some subclass of DataFrame, where the DataFrame is the raw SQL result (as it is now) plus extra methods to create bindings - this way we not break any existing code relying on .sparql - however, using the DataFrame of .sparql() would then be highly dependent on the OBDA engine, which seems awkward for such a central function
• Let .sparql() return some intermediate object from which one can obtain the bindings or the raw DataFrame
• Introduce a sibling method of .sparql() that returns a more meaningful result

from archived-sansa-query.

Please continue discussion at #47

from archived-sansa-query.