Here are some common queries I use in Postgres.

View Current Query Activity

SELECT query, state, * FROM pg_stat_activity

Drop Existing Connections Except Yours (9.2+)

SELECT pg_terminate_backend(pg_stat_activity.pid)
FROM pg_stat_activity
WHERE pg_stat_activity.datname = 'TARGET_DB' -- ← change this to your DB
  AND pid <> pg_backend_pid();

References