The problem was in the way table references are pre-filtered when
resolving a qualified field. When resolving qualified table references
we search recursively in the operands of the join. If there is
natural/using join with a merge view, the first call to find_field_in_table_ref
makes a recursive call to itself with the view as the new table reference
to search for the column. However the view has both nested_join and
join_columns != NULL so it skipped the test whether the view name matches
the field qualifier. As a result the field was found in the view since the
view already has a field with the same name. Thus the field was incorrectly
resolved as the view field.


mysql-test/r/select.result:
  Test for BUG#13127.
mysql-test/t/select.test:
  Test for BUG#13127.
sql/sql_base.cc:
  The patch contains two independent changes:
  
  - When searching for qualified fields, include merge views and information schema tables
  used with SHOW (both using TABLE_LIST::field_translation to represent result fields) in
  the test that compares the qualifying table with the name of the table reference being
  searched. This change fixes the bug.
  
  - Do not search the materialized list of columns of a NATURAL/USING join if 'table_list'
  is a stored table or merge view. Instead search directly in the table or view as if it
  is not under a natural join. This is a performance improvement since if 'table_list'
  is a stored table, then the search can utilize the name hash for table names.