How to get closest n rows for specific row in table? - sql

Question

I have a table foo with its primary key id and some other columns.
My goal is to find for instance rows with id=3 and id=4 and rows with id=6 and id=7 for row with id=5 - in case I would like to find 2 closest previous and next rows.
In case there is only one or no such rows (e.g. for id=2 there is only previous row) I would like to get only possible ones.
The problem is there can be some rows missing.
Is there a common practice to make such queries?

Answer 1

I would try the following:
SELECT * FROM table WHERE id > ? ORDER BY id ASC LIMIT 2
followed by
SELECT * FROM table WHERE id <= ? ORDER BY id DESC LIMIT 2
You may be able to combine the above into the following:
SELECT * FROM table WHERE id > ? ORDER BY id ASC LIMIT 2
UNION
SELECT * FROM table WHERE id <= ? ORDER BY id DESC LIMIT 2

Answer 2

I think this would fit your description.
Select * from table where id between #n-2 and #n+2 and id <> #n

Answer 3

One way is this:
with your_table(id) as(
select 1 union all
select 2 union all
select 4 union all
select 5 union all
select 10 union all
select 11 union all
select 12 union all
select 13 union all
select 14
)
select * from (
(select * from your_table where id <= 10 order by id desc limit 3+1)
union all
(select * from your_table where id > 10 order by id limit 3)
) t
order by id
(Here 10 is start point and 3 is n rows you want)

Answer 4

This is a possible solution by numbering all the records and fetching those where row number is 2 rows greater or lower than the selected ID.
create table foo(id int);
insert into foo values (1),(2),(4),(6),(7),(8),(11),(12);
-- using ID = 6
with rnum as
(
select id, row_number() over (order by id) rn
from foo
)
select *
from rnum
where rn >= (select rn from rnum where id = 6) - 2
and rn <= (select rn from rnum where id = 6) + 2;
id | rn
-: | -:
2 | 2
4 | 3
6 | 4
7 | 5
8 | 6
-- using ID = 2
with rnum as
(
select id, row_number() over (order by id) rn
from foo
)
select *
from rnum
where rn >= (select rn from rnum where id = 2) - 2
and rn <= (select rn from rnum where id = 2) + 2;
id | rn
-: | -:
1 | 1
2 | 2
4 | 3
6 | 4
dbfiddle here