There is/was https://en.wikipedia.org/wiki/MSQL https://en.wikipedia.org/wiki/MSQL There were also minimalist SQL interfaces to say BerkeleyDB and DBM around.

There is/was https://en.wikipedia.org/wiki/MSQL https://en.wikipedia.org/wiki/MSQL There were also minimalist SQL interfaces to say BerkeleyDB and DBM around. It was a rival of MySQL for a while. The article says "mSQL was the first low-cost SQL-based database management system" but notes citation needed. Certainly matches my memory though. Home page: https://hughestech.com.au/products/msql/ https://hughestech.com.au/products/msql/ [I thought it could run serverless but maybe that was very early versions if at all]