The common column name <str> cannot be qualified with a table
  name

  Explanation:  The name given in the error message is a common
  column name which can not be qualified.  The error occurs if
  there are columns with the same name are not specified as join
  columns in a joined table.

  User Action:  Use column renaming to make the column names
  unique or specify the column as a named join column using the
  USING clause.