Queries/executions per second

Hello,

Is there a way I can get the number of queries per second on a PostgreSQL
database? I'm talking about the average number since the server, or the
statistics collector, was started.

I have to generate a report for the database usage in my company. We chose
queries per second as one of the metrics because it could be obtained for
both MySQL (no transaction metrics are recorded) and Oracle (it can be
easily calculated). Although it's not an optimal measure of the performance
of a database, it gives an estimation of the total usage of the
infrastructure.

I know in PostgreSLQ I can get the number of transactions executed or
rolled back using pg_stat_database. But is there any way I can calculate
the number of queries/executions?

Cheers,

Daniel