docs: Update frequently-asked-questions-page.mdx (#14837)

* Update frequently-asked-questions-page.mdx

refine answer for first question, added SQL Lab query description.

* fix EOL lint

Co-authored-by: Ville Brofeldt <ville.v.brofeldt@gmail.com>

docs/src/pages/docs/frequently-asked-questions-page.mdx

@@ -24,6 +24,9 @@ will do its own _GROUP BY_ and doing the work twice might slow down performance.
 Whether you use a table or a view, the important factor is whether your database is fast enough to
 serve it in an interactive fashion to provide a good user experience in Superset.
 
+However, if you are using the SQL Lab, there is no such limitation, you can write sql query to join
+multiple tables as long as your db account has access to the tables.
+
 ### How BIG can my datasource be?
 
 It can be gigantic! Superset acts as a thin layer above your underlying databases or data engines.