There are other sessions using the database. code example

Example: view and kill postgresql connections to database

/* view connections */
SELECT * FROM pg_stat_activity;

/*-— Kill connections*/
SELECT
    pg_terminate_backend(pid)
FROM
    pg_stat_activity
WHERE
    -- don't kill my own connection!
    pid != pg_backend_pid()
    -- don't kill the connections to other databases
    AND datname = 'clinical_data';

/* kill a specific connection */     
select pg_terminate_backend(13337)