BO automatically generates the SQL query when objects are selected into query panel. When you run the query, the query is processed to database based on your connectivity.

for ex: If you run query using, Local Machine Full Client (BO reporter), the query directly connects to database through midilleware

Full Client <---> Database

If you run query using Webi, the webi browser will connects to Web Server and Webserver will proces request to Database.

WEBI <--->Web Server <---> Database