Specifies the default catalog name for an SQL user session
    in dynamically prepared and executed or interactive SQL until
    another SET CATALOG statement is issued.

    Within one multischema database, tables in different catalogs
    can be used in a single SQL statement; tables in catalogs in
    different databases cannot. If you omit the catalog name when you
    specify an object in a multischema database, SQL uses the default
    catalog name.