In addition to qualifying column names with table names or view
    names, you can qualify column names with correlation names.
    Correlation names are analogous to aliases, but they refer to
    tables instead of databases. Just as aliases provide temporary
    names for databases to qualify ambiguous table names, correlation
    names give temporary names to tables to qualify ambiguous column
    names.

    Specify a correlation name after a table name within the FROM
    clause of a select expression or DELETE statement, or in an
    UPDATE statement. Use any valid name that has not already been
    used in the FROM clause either as a correlation name or as a
    table name without a correlation name.

    You must use correlation names to qualify column names in
    statements that join a table with itself. As with table names
    and view names, however, you can always specify a correlation
    name for clarity