What is the evolutionary relationship between a bat wing and a bird wing

The bird and bat wings are analogous to each other. It mean they both have superficially similar body structure (wings) but it came from separate evolutionary origins. Analogy is a product of convergent evolution.

Although bird and bat wings are analogous, their forelimbs are homologous to each other. Their forelimbs came from a common ancestors that also had the same characteristic.