To get a list of keywords compared to SQL'92, take the keywords out of
backend/parser/keywords.c and tools/SQL_keywords.

Then run sdif with the PostgreSQL keyword file first, then the SQL'92
keywords.  Here is what I used:

sdif tools/SQL_keywords /tmp/pgkeywords |\
sed 's/</ /' | sed 's/>/ /'|sed 's/|/\
                                        /' | sort -b +0