If TEMPORARY or TEMP is specified, the source is created as a temporary source.
Temporary sources are automatically dropped at the end of a session
Temporary sources are expected to be selected by batch queries, not streaming queries.
Temporary sources currently are only used by cloud portal to preview the data during table and
source creation, so it is a internal feature and not exposed to users.
The current PR supports temporary source with minimum effort,
so we don’t care about the database name and schema name, but only care about the source name.
Temporary sources can only be shown via show sources command but not other system tables.