'Creates a new primary key on the specified columns.'

@invalidate_table_constraints
def create_primary_key(self, table_name, columns):

    if (not isinstance(columns, (list, tuple))):
        columns = [columns]
    self.execute((self.create_primary_key_string % {'table': self.quote_name(table_name), 'constraint': self.quote_name((table_name + '_pkey')), 'columns': ',    '.join(map(self.quote_name, columns))}))
