Parser should be able to handle various DUAL tables, including aliased ones

[lukaseder]

The parser currently ignores single DUAL tables in the FROM clause, and correctly translates these:

-- Oracle
SELECT 1 FROM dual

-- PostgreSQL
SELECT 1

But this doesn't work if dual is aliased, or appears in joins, table lists, etc.:

-- Oracle
SELECT 1 FROM dual x
SELECT 1 FROM dual, t

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See also:

• https://stackoverflow.com/q/78261606/521799