sql server - SQL Trigger not executing -

i have simple sql trigger cannot work. code below. trying have trigger run if "vendid" column updated in table1. trigger should write hardcoded record inventory table shown below, not doing this.

alter trigger [dbo].[table1_vendorid_modified]    on  [dbo].[table1]    after update  begin     set nocount on          if (update(vendid))     begin     insert database1.dbo.inventory     (         classid         , crtd_user         , lupd_datetime         , lupd_user         , vendid     )      select '1', 'username', '9/10/2014', 'user1', '123456abcdef' end