[求助]数据库基础方面的问题-->bygg转移

if object_id('shiyan') is not null
drop table shiyan
go
create table shiyan(col char(2))
insert into shiyan select 'a'
union select 'a'
select * from shiyan


if object_id('shiyan') is not null
drop table shiyan
go
insert into shiyan select 'a'
union all select 'a'
select * from shiyan
你把这两个放到查询分析器执行一下就知道区别了