DuckDB

Supported since 5.0.2.

Through the DuckDB (opens new window) connector, Ontop is able to construct VKGs on DuckDB database files.

Limitations & Exceptions

WARNING

DuckDB does not provide information about integrity constraints. Make sure to provide this information in order to avoid very inefficient queries. We recommend using lenses for this purpose.

• DuckDB database files prior to version 1.0 are not guaranteed to be compatible with later versions.
• Setting a default schema is not supported when connecting to DuckDB.
• Nested data types are only supported starting from version 0.7 of DuckDB.
• Accessing struct fields using the "dot operator" is not supported.

Database Connection

The following shows the content of a sample .properties file that can be used to connect Ontop to DuckDB:

jdbc.url = jdbc:duckdb:path/to/database.db
jdbc.driver = org.duckdb.DuckDBDriver

Nested Type Support

Ontop implements explicit compatibility with the DuckDB array type T[]. When used with the flatten lens, it is able to automatically infer the type of the result column.

The flatten lens cannot be used on arrays stored as JSON-encoded columns in the database. For such use cases, the column first has to be converted to an array type.

NOTE

Nested data types are only supported starting from version 0.7 of DuckDB.

Struct Access

Individual struct objects can be accessed by SQL expressions in the dialect's default way:

SELECT my_struct['my_attribute'] FROM ...

WARNING

Accessing struct fields using the "dot operator" is not supported.