According to PostgreSQL 7.1 through 9.1 (now unsupported),
ALIAS is listed as a reserved word, at least for SQL-99. Later versions do not show it - suggesting that it has been dropped as a reserved word. The old PostgreSQL docs do say "the presence of a key word does not indicate the existence of a feature." When aliasing a table or column I've seen
AS, but never
Where is (or was) the SQL keyword
ALIAS used? Was it ever in-use or only ever reserved for future-use?