@zzxbg       bit = 1
AS
BEGIN
SET NOCOUNT ON;
    WITH tb(Invoice_No, chxi, ForAccountof, NotifyParty, Consignee, gs) AS
    (
     SELECT a.Invoice_No, a.chxi, c.ForAccountof, c.NotifyParty, c.Consignee, c.gs
     from tb1
    )
   if zzxbg = 1
   begin
    ....
   end

END

  @zzxbg       bit = 1
AS
BEGIN
SET NOCOUNT ON;
    WITH tb(Invoice_No, chxi, ForAccountof, NotifyParty, Consignee, gs) AS
    (
     SELECT a.Invoice_No, a.chxi, c.ForAccountof, c.NotifyParty, c.Consignee, c.gs
     from tb1
    )
--可以这样
  select case @zzxbg when 1 then '' else '' end

END

------解决方案--------------------
不是只能接select

是with 定义了表达式后马上要使用，例如：
SQL code

declare @t table(id int)
;with m as (select 1 as col)
insert into @t select * from m

------解决方案--------------------
定义公用表表达式后，须对其进行引用。 （语法限定）