sql-server - 如何更有效地编写此查询？

Question

在我的个人资料网站上，用户可以发表评论，并对评论发表评论(就像 facebook 的 1 级)。我正在实现一些分页，因为 1 个个人资料可以有数千条评论。分页有效，但是，由于有子评论，一个简单的前 n 查询会中断对话。我只想对父注释进行分页，而不是对子注释进行分页。

表'评论' 其中有:

- commentID
- commentText
- parentCommentID
- commentOnUserID

这里的问题是我只想对父评论 (parentCommentID = 0) 进行分页。所以我写了一个查询:

select * from Comments c
where c.parentCommentID = 0 
and c.commentOnUserID = 65939 

(我省略了实际的分页查询，因为它不相关)

但我还想加载所有这些评论的子项，子项也是一个评论，但随后 parentCommentID = some commentID:

select * from comments c
where c.parentCommentID in ( * get the commentId's from the previous query)
and c.commentOnUserID = 65939

有没有一种方法可以有效地将两者合二为一的查询？

Answer 1

declare @T table(commentID int,
                 commentText varchar(max),
                 parentCommentID int,
                 commentOnUserID int)

insert into @T values
(1, 'Comment 1', 0, 1),
(2, 'Comment 2', 0, 1),
(3, 'Comment 3', 0, 1),
(4, 'Comment 4 sub 1', 1, 1),
(5, 'Comment 5 sub 1', 1, 1),
(6, 'Comment 6 sub 1', 1, 1),
(7, 'Comment 1 sub 2', 2, 1),
(8, 'Comment 1 sub 2', 2, 1),
(9, 'Comment 1 sub 3', 3, 1)

declare @UserID int = 1

;with cte as
(
  select
    T.commentID,
    T.CommentText,
    row_number() over(order by commentID) as rn
  from @T as T
  where
    T.parentCommentID = 0 and
    T.commentOnUserID = @UserID
  union all
  select   
    T.commentID,
    T.CommentText,
    C.rn
  from @T as T
    inner join cte as C
      on T.parentCommentID = C.commentID
)
select *
from cte
where rn between 1 and 2 -- use rn for pagination
order by rn, commentID

结果

commentID   parentCommentID CommentText          rn
----------- --------------- -------------------- --------------------
1           0               Comment 1            1
4           1               Comment 4 sub 1      1
5           1               Comment 5 sub 1      1
6           1               Comment 6 sub 1      1
2           0               Comment 2            2
7           2               Comment 1 sub 2      2
8           2               Comment 1 sub 2      2