The default can include the wildcard characters (%, _, [] , and [^]) if the procedure uses the parameter with the like keyword.
For example, you can modify showind to display information about the system tables if the user does not supply a parameter, like this:
create procedure showind4
@table varchar(30) = "sys%" as
select table_name = sysobjects.name,
index_name = sysindexes.name,
index_id = indid
from sysindexes, sysobjects
where sysobjects.name like @table
and sysobjects.id = sysindexes.id
