String manipulation ambiguous return type in SPARQL query

[morelator]

Hi I’m trying to build a SPARQL query using String Manipulation (Variable) Node.
In input it gets flow variable data from a table, it should replace item column with the desired query, but I get only ‘ambiguous return type’ error

[AlexanderFillbrunn]

Hi,
in your expression you need to wrap string literals in double quotes. Additionally you need to use the join() function for concatenating literals and variables. Like this:

join("select ?name where { ?instance bf2:title ", $${Sitem}$$, " . ?instance schema:name ?name }")

You can also insert line breaks with the escape sequence “\n”.
Kind regards
Alexander

[morelator]

Thank you. It worked.
The final query at the end was:
join("PREFIX bf2: <http://id.loc.gov/ontologies/bibframe/> \n prefix schema:<http://schema.org/> \n select ?name where { \n ?instance bf2:title <http://dati.cobis.to.it/instance/title/", $${Sitem}$$, "> .\n ?instance schema:name ?name \n}")