[Asterisk-Users] get value from DB directly

[unplug]

Hi,
  I want to know how I can get a value from a table.  Say, I have a
table sip_buddies for storing sip user account information.  There is
a field called 'accountcode' that I want to get its value in the dial
plan.  As I find that there is no direct way to get the value from the
table.  Does anyone can tell me how can I get its value in the dial
plan?
Thanks!