Check for constraint on table

If I check for a column's existance as follows, before adding it, how would I do the equivalent for a UNIQUE constraint?

IF NOT EXISTS (SELECT * FROM sys.columns WHERE object_id=OBJECT_ID('[Table]') AND [Name]='Column')
    ALTER TABLE [Table] 
    ADD 
    [Column] varchar(500)

From stackoverflow

• Something like this for a constraint FK_myTable (SQL 2000):

  if not exists ( select *
      from sysconstraints sc
      inner join sysobjects tbl on sc.id = tbl.id
      inner join sysobjects con on sc.constid = con.id
      where tbl.name = 'myTable' and con.name = 'FK_myTable' )
  

  jhale : I believe that sysconstraints and sysobjects have been deprecated and you are no longer supposed to use them.

  MikeW : I'm still living in a cave and using SQL 2000 :)

• select * from sys.objects where type = 'uq' and parent_object_id = OBJECT_ID('[Table]')