>e.g. name another programming language that is as valuable today as it was 20 years ago, if not moreso
If we include non-Turing-complete languages as “programming languages”, which we must for SQL to get that 20-year label since SQL wasn't Turing-complete until recursive CTEs were part of the language, then XML.
Also, even without that caveat, candidates include Bash, C, C++, Objective-C, Perl, elisp, Java, JavaScript, MATLAB, VHDL, and others. Some, while still being as useful as they were 20 years ago, are down from a peak in the intervening period, but arguably that's true of SQL, as well.
If we include non-Turing-complete languages as “programming languages”, which we must for SQL to get that 20-year label since SQL wasn't Turing-complete until recursive CTEs were part of the language, then XML.
Also, even without that caveat, candidates include Bash, C, C++, Objective-C, Perl, elisp, Java, JavaScript, MATLAB, VHDL, and others. Some, while still being as useful as they were 20 years ago, are down from a peak in the intervening period, but arguably that's true of SQL, as well.