A system includes a coordinator node and worker nodes in communication with the coordinator node. Each worker node stores data blocks. Each data block has data in a semi-structured format and each data block has an associated foreign table declaration specifying conversion of the data in the semi-structured format into a tabular format interpretable by a query language. A query processor executed by the coordinator node produces a distributed query plan in response to a query language query. The distributed query plan includes sub-queries. The sub-queries are executed by selected worker nodes of the worker nodes. The selected worker nodes use foreign table declarations to convert data in semi-structured formats into tabular formats of a distributed database to provide tabular data in response to the query language query.