Value carry forword - sql

Question

I have below SQL Query..
SELECT dbo.O3.[s.no] AS [O3_Sn.NO], dbo.O5.[s.no] AS [O5_Sn.NO], dbo.O3.O3, dbo.O5.O5,
case when dbo.O3.[s.no] > dbo.O5.[s.no] then 'true' else 'false' end as ComparisonColumn
FROM dbo.O3 INNER JOIN
dbo.O5 ON dbo.O3.[s.no] = dbo.O5.[s.no]
When I run I am getting below output..
O3_Sn.NO O5_Sn.NO O3 O5 ComparisonColumn
1 1 10 11 TRUE
2 2 12 13 TRUE
3 3 11 10 FALSE
4 4 13 11 FALSE
5 5 15 16 TRUE
6 6 10 11 TRUE
7 7 12 13 TRUE
I want to remember the value of TRUE / False and should ignore if it is repeated untill i get a reverse case i.e., for TRUE , False.. and FOR False .. TRUE
Below is the out i should get it..
O3_Sn.NO O5_Sn.NO O3 O5 ComparisonColumn New_Case_Carry_value
1 1 10 11 TRUE TRUE
2 2 12 13 TRUE NULL
3 3 11 10 FALSE FALSE
4 4 13 11 FALSE NULL
5 5 15 16 TRUE TRUE
6 6 10 11 TRUE NULL
7 7 12 13 TRUE NULL

Answer 1

You can order your output using row_number() to compare a value with a value of the previous record:
with cIntermediate as (
SELECT dbo.O3.[s.no] AS [O3_Sn.NO], dbo.O5.[s.no] AS [O5_Sn.NO], dbo.O3.O3, dbo.O5.O5,
case when dbo.O3.[s.no] > dbo.O5.[s.no] then 'true' else 'false' end
as ComparisonColumn,
rowno = row_number() over
(order by dbo.O3.[s.no], dbo.O5.[s.no], dbo.O3.O3, dbo.O5.O5)
FROM dbo.O3 INNER JOIN dbo.O5 ON dbo.O3.[s.no] = dbo.O5.[s.no]
)
select i1.*,
case when i1.ComparisonColumn = i2.ComparisonColumn then null
else i1.ComparisonColumn end as NewCaseCarryValue
from cIntermediate i1
left join cIntermediate i2 on i2.rowno=i1.rowno-1

Answer 2

Ok, I will explain the concept to you, and I am sure you will be able to figure it out for yourself.
Your final result you published with all the true and false columns, that needs to become a temporary table, like this, but with some kind of identity column:
SELECT dbo.o3.[s.no] AS [O3_Sn.NO]
,dbo.o5.[s.no] AS [O5_Sn.NO]
,dbo.o3.o3
,dbo.o5.o5
,CASE
WHEN dbo.o3.[s.no] > dbo.o5.[s.no] THEN 'true'
ELSE 'false'
END AS comparisoncolumn
, ROW_NUMBER() OVER(ORDER BY dbo.o3.[s.no]) AS ident_col
INTO #temp
FROM dbo.o3
INNER JOIN dbo.o5
ON dbo.o3.[s.no] = dbo.o5.[s.no]
Then what you need to do is to select from #temp, and self join to #temp in a similar manner as here:
SELECT a.*
, CASE WHEN a.comparisoncolumn = b.comparisoncolumn THEN NULL ELSE a.comparisoncolumn END AS final_comparisoncolumn
FROM #temp a
LEFT JOIN #temp b ON a.ident_col = b.ident_col - 1
Then do a case statement to figure out if you need to print null, or true or false.
Play around with this concept, I am sure you will be able to work it out from here.

Answer 3

You can do an left join on the table itself (SN = SN-1) and compare the ComparisonColumn