@juno I've been dealing with various incarnations of SQL Server at my day job for 20 years, mostly as a developer (and occasionally wearing the DBA hat when somebody better qualified for the job isn't around).
You have my sympathies.
Maybe you should refer the client to https://www.pg-versus-ms.com/?
@starbreaker Yeah. I think it boils down to a fear of FOSS. Anyway, they've made up their mind.
If I was independently wealthy, I'd tell the client to take a hike.