标题: SQL left join问题 [打印本页] 作者: shiyiming 时间: 2010-1-25 14:53 标题: SQL left join问题 我的code如下：
[code:2e4t8gkf]
proc sql;
create table combine(drop=fname)
as select * from test2 as a
left join link2 as b
on a.fname=b.fname and b.namedt<=a.redate<=b.nameenddt;
quit;
[/code:2e4t8gkf]
test2中有55xxxx个observations，link2里面比较少，我想把link2加到test2中去，所以用left join，但是最后发现combine里面比test2少了2万个observations，这是怎么回事啊？用什么比较好？
谢谢！作者: shiyiming 时间: 2010-1-25 23:21 标题: Re: SQL left join问题 Very interesting.
I thought the number of observations in the newly created dataset is no less than that in the left table in left join statement, whatever conditions put.