The SPARQL endpoint does not return a row if any column contains a null value

[arvindmn01]

I am using this SPARQL Query to fetech the data from PostgreSQL database.

PREFIX dcim: <http://www.w3.org/ns/r2rml/dcim_location#>
                SELECT *
                WHERE {
                ?dcim_location dcim:created ?created ;
                                dcim:custom_field_data ?custom_field_data ;
                                dcim:description ?description ;
                                dcim:last_updated ?last_updated ;
                                dcim:level ?level ;
                                dcim:lft ?lft ;
                                dcim:name ?name ;
                                dcim:parent_id ?parent_id ;
                                dcim:rght ?rght ;
                                dcim:site_id ?site_id ;
                                dcim:slug ?slug ;
                                dcim:tenant_id ?tenant_id ;
                                dcim:tree_id ?tree_id .
                }

It returns an empty table because the parent_id column contains only null values. If I replace all the nulls with some data (integers), then this query works and returns the expected table.

Additionally, I tested by replacing some of the null values with data, and in this case, the query skipped those rows that contained null values.
PS: How to add the run the command in debugging mode.

[bcogrel]

Hi @arvindmn01, you need to use an OPTIONAL block around the triple pattern defining the variable ?parent_id to handle the case it is missing.

See https://www.w3.org/TR/sparql11-query/#optionals .

Regarding logging, if you use the Docker, just define the environment ONTOP_DEBUG. With the CLI, you can adjust the logging level by editing the file log/logback.xml.