def mk_flatten_mapping(db, tables, flat_table):

    '''Creates a mapping from original column names (which may have collisions)

    to names that will be distinct among the given tables.

    This is meant to be used for several tables that are being joined together.

    @param flat_table The table for the new columns

    @return dict(orig_col=new_col, ...)

        * orig_col: sql_gen.Col(orig_col_name, orig_table)

        * new_col: sql_gen.Col(orig_col_name, flat_table)

        * All mappings use the flat_table table so its name can easily be

          changed for all columns at once

    '''

    flatten_mapping = {}

    for table in tables:

        for col in table_cols(db, table):

            col = sql_gen.as_Col(col, table)

            flatten_mapping[col] = sql_gen.Col(str(col), flat_table)

    return flatten_mapping