select news.title_news, board.boardtype, topicnums.hits from news join board on news.boardid=board.boardid join topicnums on topicnums.boardid=board.boardid
select news.title_news, board.boardtype, topicnums.hits from news join board on news.boardid=board.boardid join topicnums on topicnums.boardid=board.boardid
join是什么意思? 而且得出的结果不对
create table news(newsid int identity(1,1) not null,boardid int,title_news char(20)) create table board(boardid int not null,boardtype char(20)) create table topicnums(topicid int identity(1,1) not null,title_topicnums char(20),boardid int,hits int)insert into news select '22','aaaaa'insert into board select '22','时事新闻'insert into topicnums select 'aaaaa',22,90select b.title_news,a.boardtype,c.hits from board a join news b on a.boardid=b.boardid join topicnums c on a.boardid=c.boardid
join就是内连接,楼上几位的结果肯定是对的啦
inner join 内连接 outer join 外连接 nature join 自然连接这个问题的最简单形式:select title_news,boardtype,hits from 新闻表,新闻类表,点击记数表 where 新闻表.boardid=新闻类表.boardid and title_topicnums=title_news
用连接似乎没有必要,你写的sql到了解释器后会自动的优化。
select c.title_topicnums,b.boardtype,c.hits from news a,board b,topicnums c where a.boardid=b.boardid,b.boardid=c.boardid and a.title_news=c.title_topicnums
board.boardtype,
topicnums.hits
from news
join board on news.boardid=board.boardid
join topicnums on topicnums.boardid=board.boardid
board.boardtype,
topicnums.hits
from news
join board on news.boardid=board.boardid
join topicnums on topicnums.boardid=board.boardid
而且得出的结果不对
create table news(newsid int identity(1,1) not null,boardid int,title_news char(20))
create table board(boardid int not null,boardtype char(20))
create table topicnums(topicid int identity(1,1) not null,title_topicnums char(20),boardid int,hits int)insert into news
select '22','aaaaa'insert into board
select '22','时事新闻'insert into topicnums
select 'aaaaa',22,90select b.title_news,a.boardtype,c.hits from board a
join news b on a.boardid=b.boardid
join topicnums c on a.boardid=c.boardid
outer join 外连接
nature join 自然连接这个问题的最简单形式:select title_news,boardtype,hits
from 新闻表,新闻类表,点击记数表
where 新闻表.boardid=新闻类表.boardid
and title_topicnums=title_news
用连接似乎没有必要,你写的sql到了解释器后会自动的优化。
from news a,board b,topicnums c
where a.boardid=b.boardid,b.boardid=c.boardid and a.title_news=c.title_topicnums
这个说得好。