Use this statement to analyze what an adapter script is pushing down to the underlying data source of a virtual object.
Privileges similar to the executed query.
- Details about adapter scripts and virtual schemas are available in Virtual Schemas.
- If you access virtual objects in a query and use the EXPLAIN command, the actual query is not executed and no underlying data is transferred. The query is only compiled and optimized for pushing down as much logic as possible into the query for the underlying system. The result of that statement is a table containing the effective queries for the external systems.
- You can use the EXPLAIN command as a subselect and then process its result through SQL.
- Similar information about the details of a pushdown is available in profiling information, However, this way, it is easy to access.
SELECT pushdown_id, pushdown_involved_tables, pushdown_sql FROM
(EXPLAIN VIRTUAL SELECT * FROM vs_impala.sample_07 WHERE total_emp>10000);
|1||SAMPLE_07||IMPORT FROM JDBC AT 'jdbc:impala:<shortened>' STATEMENT 'SELECT * FROM `default`.`SAMPLE_07` WHERE 10000 < `TOTAL_EMP`'|