Question

I am working on a Data Warehouse project and the client provides daily sales data. On-hand quantities are provided in most lines but are often missing. I need help on how to fill those missing values based on prior OH and sales information.

Here’s a sample data:

Line#  Store  Item  OnHand  SalesUnits  DateKey
-----------------------------------------------
1      001    A     100     20          1       
2      001    A     80      10          2       
3      001    A     null    30          3       --[OH updated with 70 (80-10)]
4      001    A     null    5           4       --[OH updated with 40 (70-30)]
5      001    A     150     10          5       --[OH untouched]
6      001    B     null    4           1       --[OH untouched - new item]
7      001    B     80      12          2       
8      001    B     null    10          3       --[OH updated with 68 (80-12]

Lines 1 and 2 are not to be updated because OnHand quantities exist.
Lines 3 and 4 are to be updated based on their preceding rows.
Line 5 is to be left untouched because OnHand is provided.
Line 6 is to be left untouched because it is the first row for Item B

Is there a way I can do this in a set operation? I know I can do it easily using a fast_forward cursor but it will take a long time (15M+ rows).

Thanks for your help!

Answer 1

Test data:

declare @t table(
Line# int,  Store char(3),  Item char,  OnHand int,  SalesUnits int, DateKey int
)

insert @t values
(1,  '001',  'A',  100,   20, 1),
(2,  '001',  'A',  80 ,   10, 2),
(3,  '001',  'A',  null,  30, 3),
(4,  '001',  'A',  null,   5, 4),
(5,  '001',  'A',  150,   10, 5),
(6,  '001',  'B',  null,   4, 1),
(7,  '001',  'B',  null,   4, 2),
(8,  '001',  'B',  80,    12, 3),
(9,  '001',  'B',  null,  10, 4)

Script to populate not using cursor:

;with a as
(
select Line#,  Store,  Item,  OnHand,  SalesUnits, DateKey, 1 correctdata from @t where DateKey = 1
union all
select t.Line#,  t.Store,  t.Item,  coalesce(t.OnHand, a.onhand - a.salesunits),  t.SalesUnits, t.DateKey, t.OnHand from @t t
join a on a.DateKey = t.datekey - 1 and a.item = t.item and a.store = t.store
)
update t
set OnHand = a.onhand 
from @t t join a on a.line# = t.line#
where a.correctdata is null

Script to populate using cursor:

declare @datekey int, @store int, @item char, @Onhand int, 
@calculatedonhand int, @salesunits int, @laststore int, @lastitem char

DECLARE sales_cursor 
CURSOR FOR  
SELECT datekey+1, store, item, OnHand -SalesUnits, salesunits
FROM @t sales  
order by store, item, datekey

OPEN sales_cursor;  
FETCH NEXT FROM sales_cursor  
INTO @datekey, @store, @item, @Onhand, @salesunits

WHILE @@FETCH_STATUS = 0 
BEGIN  
SELECT @calculatedonhand = case when @laststore = @store and @lastitem = @item 
then coalesce(@onhand, @calculatedonhand - @salesunits) else null end
,@laststore = @store, @lastitem = @item

UPDATE s
SET onhand=@calculatedonhand
FROM @t s
WHERE datekey = @datekey and @store = store and @item = item
and onhand is null and @calculatedonhand is not null

FETCH NEXT FROM sales_cursor  
INTO @datekey, @store, @item, @Onhand, @salesunits

END 
CLOSE sales_cursor; 
DEALLOCATE sales_cursor; 

I recommand you use the cursor version, I doubt you can get a decent performance using the recursive query. I know people in here hate cursors, but when your table has that size, it can be the only solution.