change default database to PostgreSQL because it has a more friendly output for running EXPLAIN
change default database to PostgreSQL because it has a more friendly output for running EXPLAIN

cmu-db/cmdbac,cmu-db/cmdbac,cmu-db/db-webcrawler,cmu-db/cmdbac,cmu-db/db-webcrawler,cmu-db/cmdbac,cmu-db/db-webcrawler,cmu-db/db-webcrawler,cmu-db/cmdbac,cmu-db/db-webcrawler