ansible playbook to run command on multiple servers with multiple databases per server

I need a host inventory and Ansible playbook for two remote database servers.
host1 will have ansible_user=db2inst1
host1 will have three databases : sample , test and playdb
host2 will have ansible_user=testinst
host2 will have 2 databases: mydb and meatdb

I want an ansible playbook that will be able to connect to each database one by one (loop) on each server with become_user : {{ ansible_user}
I will like to enable passwordless connection from the controller to the target servers. (ssh -keygen)

i want to run the playbook as : ansible-playbook -i inventory run-db2-command.yml

The preferred database will be IBM DB2.