There was an SQL layer but performance was sub-par IIRC. There was also a blog post somewhere explaining why it's probably not a good idea to build an SQL layer on top of a KV store, devil in details, etc.
Not sure what to think of it, I'm not a DB expert by any means but the post sounds plausible enough and the SQL layer is discontinued AFAIK. I guess with each new abstraction layer you leave some perf on the table.
It's not a very good analysis. The only reason there isn't a good OLTP SQL engine on top of FDB is that no one has invested the considerable resources and expertise to build one. The FDB SQL Layer was on its way, but Apple prioritized other things. Snowflake built a world class analytic SQL database on FDB and the door is still open for someone to do OLTP. There might even be room for two different designs (one more like Akiban/SQL Layer or F1, competing with Spanner, and one more like Aurora, with a more familiar performance envelope but slightly less scalability)
