The fix for bug 169079 has removed the item SQL from the Data Provider dialog. Therefore the documentation has to be adapted. That is to remove `LibreOfficeDev Base files` from the first sentence in https://help.libreoffice.org/26.2/en-US/text/scalc/01/data_provider.html and from section https://books.libreoffice.org/en/CG252/CG25215-CalcAsADatabase.html#toc12 in the Calc Guide.
Olivier Hallot committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/help/commit/92f8036ca9fe58834e6bbe3ff1d765382d337bb7 tdf#169089 Base files not supported by data provider