The first SQL ISO standard is from 1987. Oracle's first commercial SQL DBMS came out eight years earlier in 1979.
In 1987, Oracle was already the largest database vendor and IBM's database business never recovered from that setback.
That said, I don't know if Oracle had some sort of licensing agreement with IBM during those early years. The question is what any such agreement would have looked like in light of the recent legal opinions on copyright.
Contrary to FOSS myths, SQL ISO standards aren't free and don't write by themselves, Oracle had a seat at the table just like everyone else that matters on the RDMS space.
In 1987, Oracle was already the largest database vendor and IBM's database business never recovered from that setback.
That said, I don't know if Oracle had some sort of licensing agreement with IBM during those early years. The question is what any such agreement would have looked like in light of the recent legal opinions on copyright.