TSQL Challenge 12 was a relatively easier one. The participants were given month-wise score values and were asked to complete the sequence by creating entries for missing month.
Here’s the sample input:
YearMonth Score ----------- ----------- 200903 100 200803 95 200802 99 200801 100 200711 100
And here’s the desired output. Notice that the score of last month is replicated in each of the missing rows:
YearMonth Score ----------- ----------- 200908 100 200907 100 200906 100 200905 100 200904 100 200903 100 200902 95 200901 95 200812 95 200811 95 200810 95 200809 95 200808 95 200807 95 200806 95 200805 95 200804 95 200803 95 200802 99 200801 100 200712 100 200711 100
The script to generate sample data is provided below:
DECLARE @Scores TABLE ( YearMonth INT, Score INT ) INSERT @Scores VALUES(200903, 100) INSERT @Scores VALUES(200803, 95) INSERT @Scores VALUES(200802, 99) INSERT @Scores VALUES(200801 ,100) INSERT @Scores VALUES(200711, 100)
Solution
I once blogged about creating a sequence of numbers/dates using a recursive CTE in this post. The same technique can be used here. However, since the YearMonth column in the sample data is integer, we have two choices:
- Convert it to DateTime and apply T-SQL DateTime functions
- Leave it as Integer and apply some intelligent arithmetic
I am providing both the solutions here. Note that the first solution will be slower due to overhead of casting and applying T-SQL scalar functions.
The first solution: Converting to DateTime
;with cte as
(
select score, Cast(Cast(YearMonth as varchar)+'01' as datetime) as dateVal
from @scores
union all
select score, dateadd(month, 1, dateval)
from cte
where not exists
--the resultant YearMonth value should not lie in the original table
( select 1 from @scores s where s.YearMonth = cast( left(convert(varchar, dateadd(month, 1, cte.dateval), 112), 6) as int) )
--stop at current month
and dateadd(month, 1, cte.dateval) < getdate()
)
select left(convert(varchar, dateval, 112), 6) as yearmonth, score
from cte
order by dateval desc
Explanation:
Here I am simply converting the integer YearMonth column to a datetime dateval column by appending 01 to the end (so a 200901 becomes 20090101 that can easily be cast to a dateTime) and then finding subsequent dates by adding one month in each CTE iteration.
The second solution: Integer Arithmetic
;with cte as
(
select YearMonth, Score
from @Scores
union all
select YearMonth + YearMonth % 100 / 12 * 88 + 1 as YearMonth, Score
from cte
where not exists
--the resultant YearMonth value should not lie in the original table
( select s.YearMonth from @Scores s where s.YearMonth = (cte.YearMonth + cte.YearMonth % 100 / 12 * 88 + 1) )
--stop at current month
and cte.YearMonth < month(getdate()) + year(getdate())*100
)
select *
from cte
order by YearMonth desc
Explanation:
The important point is to increment the value of YearMonth correctly. So 200811 should get incremented to 200812 but 200812 should get incremented to 200901. This isn’t difficult if we introduce a case statement like this:
YearMonth + (Case When YearMonth%100 < 12 Then 1 Else 89 End)
But I wanted to do this purely using arithmetic with no Case statements, so I came up with this formula:
(YearMonth % 100 / 12 * 88) + 1
Note that the factor (YearMonth % 100 / 12 * 88) will reduce to zero for all values from January to November, i.e. from 200801 to 200811.
I hope you enjoyed the solution.
Update:
It was pointed out in one of the comments by Rakesh that the solution could reach the default limit of recursion which is 100. In order to avoid this, we need to add option (maxrecursion 12,000) in the final select statement. Then, we can have 10,000 years missing between two adjacent entries. Thanks, Rakesh.
... select * from cte order by YearMonth desc option (maxrecursion 12,000)
