SQL - Where campo=todo

ALTER PROCEDURE  QUERY1

	@ZONA nvarchar(20) ,@SEDE nvarchar(20)

AS

Select *  from data  where [zona]=@ZONA and [sede]=@sede

GO

como podria hacer en este escenario

cuando @ZONA='TODOS' o  @SEDE='TODOS'

ALTER PROCEDURE QUERY1

@ZONA nvarchar(20) ,@SEDE nvarchar(20)

AS

IF (@ZONA != 'TODOS' AND @SEDE != 'TODOS')

  Select * from data where [zona]=@ZONA and [sede]=@sede

ELSE

 BEGIN

   IF (@ZONA = 'TODOS')

     Select * from data where [sede]=@sede

   ELSE

     Select * from data where [zona]=@ZONA

END

ALTER PROCEDURE QUERY1

@ZONA nvarchar(20) ,@SEDE nvarchar(20)

AS

Select * from data

IF (@ZONA != 'TODOS' AND @SEDE != 'TODOS')

 where [zona]=@ZONA and [sede]=@sede

ELSE

IF (@ZONA = 'TODOS')

 where [sede]=@sede

ELSE

where [zona]=@ZONA

END

GO