How to select just the third or fourth row in SQL Server - sql

Question

I am having a little bit of trouble figuring out a way to select just the third or fourth row in a query I am writing, any help would be greatly appreciated.
This is an example of the code I came up with, this however only selects the first row.
Left Outer Join (select ap_attachments.ap_table_key, ap_description, ap_creation_date, ap_creation_time, ap_file_name, ap_attach_id
from ap_attachments
inner join (select Min(ap_attachment_id) ap_attach_id, ap_table_key
from ap_attachments
where ap_file_name like '%jpg%'
group by ap_table_key) C
On ap_attachments.ap_attachment_id = C.ap_attach_id) apImgThree_attach
On apImgTwo_attach.ap_table_key = order_link.to_order_id

Answer 1

You can do this with the ROW_NUMBER() function:
select ap_attachment_id, ap_table_key,ROW_NUMBER() OVER(PARTITION BY ap_table_key ORDER BY ap_attachment_id) AS RN
from ap_attachments
where ap_file_name like '%jpg%'
Then you can specify which row you'd like to return using the RN value. This may require some adapting depending on your source data, the DENSE_RANK() function may be more appropriate.
The ROW_NUMBER() function assigns a number to each row. PARTITION BY is optional, but used to start the numbering over for each value in that group, ie: if you PARTITION BY Some_Date then for each unique date value the numbering would start over at 1. ORDER BY of course is used to define how the counting should go, and is required in the ROW_NUMBER() function.

Answer 2

Look up the docs on lead and lag. You can also use the PARTITION clause to create the window within a specific date, for example;
declare #table table(
[flower] [sysname]);
insert into #table
([flower])
values (N'rose'),
(N'tulip'),
(N'chamomile'),
(N'lily');
select [flower] from #table order by [flower];
select [flower]
, lag ([flower]
, 1
, 0)
over (
order by [flower] desc) as [previous_flower]
, lead ([flower]
, 1
, 0)
over (
order by [flower] desc) as [next_flower]
from #table;