Is there a database that speaks pure SQL?

Question

My understanding is that SQL is the standardized basic framework for quite a variety of different SQL flavors like MS SQL, MySQL, PostgreSQL, ...

But all of these different flavors introduce a certain level of incompatibility between each other. So my question is are there actually databases systems that speak "pure" (as in only those things described in ISO/IEC 9075) SQL and don't introduce own things?

Answer 1

It indeed seems like the only database system that speaks pure SQL are the systems that IBM used to develop SQL on.

For SEQUEL this seems to be IBM System R, and

for SQL this seems to be IBM SQL/DS.

Even the predecessor of IBM SQL/DS, IBM DB2 had some non standard compliant features.