Since there weren't any commercial relational databases available pre-SQL, this is quite true. Codd wrote a couple of query languages before, but they apparent

Since there weren't any commercial relational databases available pre-SQL, this is quite true. Codd wrote a couple of query languages before, but they apparently weren't usable by mere mortals. SQL is over 40 years old, and still dominates. The most recent contenders had to position themselves in terms of SQL (NoSQL).