update_3 error : db_drop_column

I have drupal 5.7 and advanced poll beta4.

When I tried to upgrade it to beta6, I got such message:

( ! ) Fatal error: Call to undefined function db_drop_column() in /home/maho/workspace/longturn.org/modules/_my/advpoll/advpoll.install on line 185
Call Stack
# Time Memory Function Location
1 0.0019 451328 {main}( ) ../update.php:0
2 0.1831 25150208 update_do_update_page( ) ../update.php:809
3 0.1831 25150208 update_do_updates( ) ../update.php:471
4 0.2119 25660688 update_data( ) ../update.php:426
5 0.2119 25660688 module_invoke( ) ../update.php:291
6 0.2120 25660688 call_user_func_array ( ) ../module.inc:386
7 0.2120 25660688 advpoll_update_3( ) ../module.inc:0

Database: postgres 8.3