You can specify a correlation name following a table or a view,
    and you must specify a correlation name for a derived table in
    the FROM clause to qualify column names in other parts of the
    select expression. If you do not explicitly specify a correlation
    name, SQL implicitly specifies the table name or view name as a
    correlation name. The same correlation name may not be specified
    more than once, either explicitly or implicitly.

    The correlation name may also rename columns when specified with
    a derived table. Therefore, the number of columns in the table to
    the left of the correlation name must match the number of columns
    specified to the right of the correlation name.