没看懂语句，求解释

没看懂语句，求解释~在线等
泡论坛，看了一条小F姐姐的问题解答,如下：
表T的数据如下，
A B
-------
A1 B1
A1 B2
A2 B1
A3 B2

希望得到
A B
--------
A1 B1
A2 B2
A3

SQL code

;with f as(select id=row_number()over(partition by a order by getdate()),* from tb)select  isnull(a.a,'') as a,isnull(b.b,'') as bfrom(select px=row_number()over(order by getdate()),* from (select distinct id,a from f where id=1)t)aleft join (select px=row_number()over(order by getdate()),* from (select distinct id,b from f where id=1)t)bon a.px=b.px

SQL code

;with f as(select id=row_number()over(partition by a order by getdate()),* from tb   --按照A列排序)select  isnull(a.a,'') as a,isnull(b.b,'') as b  --A列，B列有值的直接列出，没有的就显示为空字符from(select px=row_number()over(order by getdate()),* from (select distinct id,a from f where id=1)t)a  --取出按照A列中的序列（不重复的）left join --俩个序列进行连接 (select px=row_number()over(order by getdate()),* from (select distinct id,b from f where id=1)t)b  --取出按照B列中的序列（不重复的）on a.px=b.px