'Deletes an index created with create_index.
This is possible using only columns due to the deterministic
index naming function which relies on column names.'

@invalidate_table_constraints
def delete_index(self, table_name, column_names, db_tablespace=''):

    if isinstance(column_names, string_types):
        column_names = [column_names]
    name = self.create_index_name(table_name, column_names)
    sql = (self.drop_index_string % {'index_name': self.quote_name(name), 'table_name': self.quote_name(table_name)})
    self.execute(sql)
