By default, psql will keep track of all recent queries and commands in the
.psql_history file in your home directory.
When in a psql session, you can hit the Up key to go back through the
history to find a previously entered query. That means you can quickly retrieve
and rerun past queries.
However the default psql configuration means that your history can contain
queries from a psql session with another database that don't make sense in
the context of the current database.
You can keep these query histories separate by configuring psql to use
separate history files per database. This can be done by adding the following
line to your ~/.psqlrc file.
\set HISTFILE ~/.psql_history-:DBNAME