触发器小问题？请教！！！

[aierong]

/*创建销售表的修改触发器，用于向库存表（storage）中修改stor_number字段（库存量）数据 */

create trigger update_stor_number
on sell
for update as
begin
/*先加上表（storage）中stor_number字段（库存量）数据 */
update storage
set stor_number=stor_number+(select sum(sell_number) from deleted group by prod_id)
from deleted
where deleted.prod_id=storage.prod_id
/*先减去表（storage）中stor_number字段（库存量）数据 */
update storage
set stor_number=stor_number-(select sum(sell_number) from inserted group by prod_id)
from inserted
where inserted.prod_id=storage.prod_id
end
go

有一个修改触发器，在表被修改时，即触发
现在我想在修改sell表里的字段a和字段b和字段c才触发它，该怎么写触发。

[愉快的登山者]

if update(a) or update(b) or update(c)
begin
......
end

[dlkfth]

楼上的对呀