IS REJECTED.

Analysis
========

View creation with named columns over UNION is rejected.
Consider the following view definition:

CREATE VIEW v1 (fld1, fld2) AS SELECT 1 AS a, 2 AS b
UNION ALL SELECT 1 AS a, 1 AS a;

A 'duplicate column' error was reported due to the duplicate
alias name in the secondary SELECT. The VIEW column names
are either explicitly specified or determined from the
first SELECT (which can be auto generated if not specified).
Since a duplicate column name check was performed even
for the secondary SELECTs, an error was reported.

Fix
====

Check for duplicate column names only for the named
columns if specified or only for the first SELECT.