Optimize query joining multiple tables

We have many queries that require to join multiple same tables. It takes undesireably long time for Metabase to get result for such queries.

The tables are already created and it is hard to change the tables' structure (e.g., create a big physical table that contains all the columns of these tables)

Can anyone point me some tricks/links for optimizing the query speed? Thanks

Hi @xuheng925
View the SQL and then prepend the query with EXPLAIN ANALYZE to understand if your database is correctly indexed or if it uses temporary tables, which is very bad for performance.