Select nearest date on the basis of ID in SQL - sql

Question

I have two table Dispense & Pro Table, I want to select all rows from Dispense table and nearest Shipment date from Pro table.
Dispense Table
ID Dispense date Row ID
604743 10/18/2016 1
604743 11/4/2016 2
604743 11/28/2016 3
604743 12/16/2016 4
Pro table
ID Shipment Date Row ID
604743 11/1/2016 1
604743 11/19/2016 2
604743 11/21/2016 3
604743 11/28/2016 4
604743 12/13/2016 5
Output Needed
ID Dispense date Pre Ship date
604743 10/18/2016 NULL
604743 11/4/2016 11/1/2016
604743 11/28/2016 11/19/2016
604743 12/16/2016 12/13/2016
Reason for NULL: Because less than 10/18 dispense date no nearest date in Shipping date in Pro Table

Answer 1

I tried with recursive CTE, but they don't all to use the anchor in a subquery.
So a while-loop is the best I could do.
The script allows for several Dispense or Pro at same date, see the comments on which part you can throw out if that is not allowed by constraints.
--- Dispense_Date must not be unique
declare #Dispense table(
ID int not null,
Dispense_Date date not null,
Row_ID int not null identity primary key
)
-- Shipment_Date must not be unique
declare #Pro table(
ID int not null,
Shipment_Date date not null,
Row_ID int not null identity primary key
)
declare #Result table(
ID int not null,
Dispense_Date date not null,
Dispense_Row_ID int not null unique,
Shipment_Date date not null,
Pro_Row_ID int not null unique,
dayDiff int not null,
Row_ID int not null identity primary key,
iter int not null
)
insert into #Dispense(ID, Dispense_Date)
values (604743, '10/18/2016'),
(604743, '11/4/2016'),
/* (604743, '11/26/2016'),
(604743, '11/27/2016'),
(604743, '11/27/2016'),
(604743, '11/28/2016'), */
(604743, '11/28/2016'),
(604743, '12/16/2016')
insert into #Pro(ID, Shipment_Date)
values (604743, '11/1/2016'),
/* (604743, '11/16/2016'),
(604743, '11/19/2016'), */
(604743, '11/19/2016'),
(604743, '11/21/2016'),
(604743, '11/28/2016'),
(604743, '12/13/2016')
declare #iter int = 0
while exists(
select 1
from #Dispense Dispense
inner join
#Pro Pro
on Pro.ID = Dispense.ID
and
Pro.Shipment_Date < Dispense.Dispense_Date
where not exists(
select 1
from #Result Result
where Result.Dispense_Row_ID = Dispense.Row_ID
or
Result.Pro_Row_ID = Pro.Row_ID
)
)
begin
set #iter = #iter + 1
;
with distance(
ID, Dispense_Row_ID, Dispense_Date, Pro_Row_ID, Shipment_Date, dayDiff
) as(
select Dispense.ID,
Dispense.Row_ID Dispense_Row_ID,
Dispense.Dispense_Date,
Pro.Row_ID Pro_Row_ID,
Pro.Shipment_Date,
DATEDIFF(DAY, Pro.Shipment_Date, Dispense.Dispense_Date) dayDiff
from #Dispense Dispense
inner join
#Pro Pro
on Pro.ID = Dispense.ID
and
Pro.Shipment_Date < Dispense.Dispense_Date
where not exists(
select 1
from #Result Result
where Result.Dispense_Row_ID = Dispense.Row_ID
or
Result.Pro_Row_ID = Pro.Row_ID
)
)
insert into #Result(ID, Dispense_Row_ID, Dispense_Date, Pro_Row_ID, Shipment_Date, daydiff, iter)
select Dispense.ID,
Dispense.Row_ID Dispense_Row_ID,
Dispense.Dispense_Date,
distance.Pro_Row_ID,
distance.Shipment_Date,
distance.dayDiff,
#iter
from #Dispense Dispense
inner join
distance
on distance.Dispense_Row_ID = Dispense.Row_ID
and
not exists(
select 1
from distance dtExists
where dtExists.ID = distance.ID
and
dtExists.Shipment_Date = distance.Shipment_Date
and
(
dtExists.dayDiff < distance.dayDiff
-- below OR not needed if Dispense_Date and Shipment_Date are unique
or
(
dtExists.dayDiff = distance.dayDiff
and
(
dtExists.Pro_Row_ID < distance.Pro_Row_ID
or
(
dtExists.Pro_Row_ID = distance.Pro_Row_ID
and
dtExists.Dispense_Row_ID < distance.Dispense_Row_ID
)
)
)
)
)
and
not exists(
select 1
from distance dtExists
where dtExists.ID = distance.ID
and
dtExists.Dispense_Date = distance.Dispense_Date
and
(
dtExists.dayDiff < distance.dayDiff
-- below OR not needed if Dispense_Date and Shipment_Date are unique
or
(
dtExists.dayDiff = distance.dayDiff
and
(
dtExists.Pro_Row_ID < distance.Pro_Row_ID
or
(
dtExists.Pro_Row_ID = distance.Pro_Row_ID
and
dtExists.Dispense_Row_ID < distance.Dispense_Row_ID
)
)
)
)
)
end
select Dispense.ID,
Dispense.Row_ID Dispense_Row_ID,
Dispense.Dispense_Date,
Result.Pro_Row_ID,
Result.Shipment_Date,
Result.dayDiff,
Result.iter
from #Dispense Dispense
left join
#Result Result
on Result.Dispense_Row_ID = Dispense.Row_ID
order by Dispense.ID,
Dispense.Dispense_Date,
Result.Shipment_Date,
Result.Dispense_Row_ID,
Result.Pro_Row_ID