title: Only ALTER a TRIGGER if is exists
body: <p>I am implementing an auditing system on my database. It uses triggers on each table to log changes.
  I need to make modifications to these triggers and so am producing ALTER scripts for each one.
  What I'd like to do is only have these triggers be altered if they exist, ideally like so:</p>
  
  <pre><code>IF EXISTS (SELECT * FROM sysobjects WHERE type = 'TR' AND name = 'MyTable_Audit_Update')
  BEGIN
  ALTER TRIGGER [dbo].[MyTable_Audit_Update] ON [dbo].[MyTable]
   AFTER Update
  ...
  END
  </code></pre>
  
  <p>However when I do this I get an error saying "Invalid syntax near keyword TRIGGER"</p>
  
  <p>The reason that these triggers may not exist is that auditing can be enabled/disabled on tables which the end user can specify. This involves either creating or dropping the triggers. I am unable to make the changes to the triggers upon creation as they are dynamically created and so I must still provide a way altering the triggers should they exist.</p>