SQL Get closest value to a number - sql

Question

I need to find the closet value of each number in column Divide from the column Quantity and put the value found in the Value column for both Quantities.
Example:
In the column Divide the value of 5166 would be closest to Quantity column value 5000. To keep from using those two values more than once I need to place the value of 5000 in the value column for both numbers, like the example below. Also, is it possible to do this without a loop?
Quantity Divide Rank Value
15500 5166 5 5000
1250 416 5 0
5000 1666 5 5000
12500 4166 4 0
164250 54750 3 0
5250 1750 3 0
6250 2083 3 0
12250 4083 3 0
1750 583 2 0
17000 5666 2 0
2500 833 2 0
11500 3833 2 0
1250 416 1 0

Answer 1

There are a couple of answers here but they both use ctes/complex subqueries. There is a much simpler/faster way by just doing a couple of self joins and a group-by
https://www.db-fiddle.com/f/rM268EYMWuK7yQT3gwSbGE/0
select
min(min.quantity) as minQuantityOverDivide
, t1.divide
, max(max.quantity) as maxQuantityUnderDivide
, case
when
(abs(t1.divide - coalesce(min(min.quantity),0))
<
abs(t1.divide - coalesce(max(max.quantity),0)))
then max(max.quantity)
else min(min.quantity) end as cloestQuantity
from t1
left join (select quantity from t1) min on min.quantity >= t1.divide
left join (select quantity from t1) max on max.quantity < t1.divide
group by
t1.divide

Answer 2

If I understood the requirements, 5166 is not closest to 5000 - it's closes to 5250 (delta of 166 vs 84)
The corresponding query, without loops, shall be (fiddle here: https://dbfiddle.uk/?rdbms=sqlserver_2017&fiddle=be434e67ba73addba119894a98657f17).
(I added a Value_Rank as it's not sure if you want Rank to be kept or recomputed)
select
Quantity, Divide, Rank, Value,
dense_rank() over(order by Value) as Value_Rank
from
(
select
Quantity, Divide, Rank,
--
case
when abs(Quantity_let_delta) < abs(Quantity_get_delta) then Divide + Quantity_let_delta
else Divide + Quantity_get_delta
end as Value
from
(
select
so.Quantity, so.Divide, so.Rank,
-- There is no LessEqualThan, assume GreaterEqualThan
max(isnull(so_let.Quantity, so_get.Quantity)) - so.Divide as Quantity_let_delta,
-- There is no GreaterEqualThan, assume LessEqualThan
min(isnull(so_get.Quantity, so_let.Quantity)) - so.Divide as Quantity_get_delta
from
SO so
left outer join SO so_let
on so_let.Quantity <= so.Divide
--
left outer join SO so_get
on so_get.Quantity >= so.Divide
group by so.Quantity, so.Divide, so.Rank
) so
) result
Or, if by closest you mean the previous closest (fiddle here: https://dbfiddle.uk/?rdbms=sqlserver_2017&fiddle=b41fb1a3fc11039c7f82926f8816e270).
select
Quantity, Divide, Rank, Value,
dense_rank() over(order by Value) as Value_Rank
from
(
select
so.Quantity, so.Divide, so.Rank,
-- There is no LessEqualThan, assume 0
max(isnull(so_let.Quantity, 0)) as Value
from
SO so
left outer join SO so_let
on so_let.Quantity <= so.Divide
group by so.Quantity, so.Divide, so.Rank
) result

Answer 3

You don't need a loop, basically you need to find which is lowest difference between the divide and all the quantities (first cte). Then use this distance to find the corresponding record (second cte) and then join with your initial table to get the converted values (final select)
;with cte as (
select t.Divide, min(abs(t2.Quantity-t.Divide)) as ClosestQuantity
from #t1 as t
cross apply #t1 as t2
group by t.Divide
)
,cte2 as (
select distinct
t.Divide, t2.Quantity
from #t1 as t
cross apply #t1 as t2
where abs(t2.Quantity-t.Divide) = (select ClosestQuantity from cte as c where c.Divide = t.Divide)
)
select t.Quantity, cte2.Quantity as Divide, t.Rank, t.Value
from #t1 as t
left outer join cte2 on t.Divide = cte2.Divide