What is the best way to duplicate rows based on multiple columns? - sql

Question

I have the following table below:
ID Start_Repeat_1 End_Repeat_1 Start_Repeat_2 End_Repeat_2
A 3 7 2 5
B 1 4 2 5
My goal is to duplicate "A" 5 times and "B" 4 times with the output below
ID Repeat_1 Repeat_2
A 3 2
A 4 3
A 5 4
A 6 5
A 7 NULL
B 1 2
B 2 3
B 3 4
B 4 5
The logic is that "A" needs to be duplicated with numbers between 3 and 7 in one column and numbers between 2 and 5 in another column so it needs to be duplicated at least 5 times.
The version below would also do. The order between the two columns does not matter.
ID Repeat_1 Repeat_2
A 3 2
A 7 5
A 6 3
A 5 NULL
A 4 4
Can someone help me with this using SQL Server 2018?
The dataset size is about 10,000 rows and each row is duplicated at most 10 times with a total of 10 columns like this
ID Repeat_1 Repeat_2 Repeat_3 Repeat_4 Repeat_10
A 3 2 1 1 1
B 7 5 1 1 1

Answer 1

You need to make use of a tally table. In the following solution, I have use a recursive cte to generate one.
Alternatively you can use a recursive cte to generate one on the fly
-- Tally Table
create table tally
(
n int
)
-- generate 1000 numbers for tally table
with cte as
(
select n = 0
union all
select n = n + 1
from cte
where n < 1000
)
insert into tally (n)
select n
from cte
The cross apply is to find the maximum difference between the repeat_1 or 2 etc.
-- The query
select t.ID,
Repeat_1 = case when n.n <= (End_Repeat_1 - Start_Repeat_1)
then t.Start_Repeat_1 + n.n
end,
Repeat_2 = case when n.n <= (End_Repeat_2 - Start_Repeat_2)
then t.Start_Repeat_2 + n.n
end,
Repeat_3 = case when n.n <= (End_Repeat_3 - Start_Repeat_3)
then t.Start_Repeat_3 + n.n
end
from tbl t
cross apply
(
select m = max(d)
from (
values
(End_Repeat_1 - Start_Repeat_1 + 1),
(End_Repeat_2 - Start_Repeat_2 + 1),
(End_Repeat_3 - Start_Repeat_3 + 1)
) n (d)
) m
inner join tally n on n.n >= 0
and n.n < m.m
dbfiddel demo

Answer 2

you can use recursive cte :
with cte as (
select * from test
union all
select Id
, case when Start_Repeat_1 + 1 > End_Repeat_1 then null else Start_Repeat_1 + 1 end
,End_Repeat_1
,case when Start_Repeat_2+ 1 > End_Repeat_2 then null else Start_Repeat_2+ 1 end
,End_Repeat_2
from cte
where Start_Repeat_1 <= End_Repeat_1 and Start_Repeat_2 <= End_Repeat_2
)
select ID,Start_Repeat_1,Start_Repeat_2
from cte
where coalesce(Start_Repeat_1,Start_Repeat_2) is not null
order by ID
ID | Start_Repeat_1 | Start_Repeat_2
:- | -------------: | -------------:
A | 3 | 2
A | 4 | 3
A | 5 | 4
A | 6 | 5
A | 7 | null
B | 1 | 2
B | 2 | 3
B | 3 | 4
B | 4 | 5
db<>fiddle here