The Rise and Fall of Ashton-Tate

I'm surprised the article didn't mention 2nd-place competitor product R:Base. R:Base was a pretty good implementation of SQL, for example it supported the INTERSECT command as I recall.

"In spite of its relative ease of use and ability to create useful forms and reports, the first R:Base did not have a conventional programming language, but instead relied on SQL statements to accept input and produce output. The lack of a complete programming language meant that the product was not well received by some portions of the market. This may have helped the early, barely relational, dBASE products to become dominant. The product was quickly upgraded to include Added Variables and a conventional programming Language (IF, WHILE, etc.) to the original SQL based language The update was released as R:Base 4000 Version 1.1 in March 1984. R:Base became the second most popular DOS database in the PC market (behind dBASE).[citation needed]"

https://en.wikipedia.org/wiki/R:BASE