Getting rowcount for a column based on values from another column - sql

Question

I have two tables, T1 AND T2.
T1 with following columns: Id, TypeofValue, Year, value
Typeofvalue can have 2 values
1 - indicates Actual
2 - indicates Target
T2 With following column: NoOfRecordsToDisplay
I need to fetch the number of records (if existing) for Target corresponding to an Id.
However, the catches are:
Sometimes Target value might not be present for a year
I need to get only last records for targets on the basis of NoOfRecordsToDisplay (The number of records to display comes from T2) for actual
Example1:
NoOfRecordsToDisplay =3, ID =123
The data below should return 3 as we have 3 non null values for target for last 3 years -2015, 2014,2013 in this case
Id TypeofValue Year Value
123 1 2015 55
123 1 2014 56
123 1 2013 57
123 1 2012 58
123 2 2015 50
123 2 2014 50
123 2 2013 50
123 2 2012 50
124 1 2015 55
124 1 2014 56
124 1 2013 57
124 1 2012 58
124 2 2015 50
124 2 2014 50
124 2 2013 50
124 2 2012 50
Another dataset -
NoOfRecordsToDisplay =3, ID =123
The data below should return 0, as we have no values for target for last 3 years -2015, 2014,2013
Id TypeofValue Year Value
123 1 2015 55
123 1 2014 56
123 1 2013 57
123 1 2012 58
123 2 2012 50
124 1 2015 55
124 1 2014 56
124 1 2013 57
124 1 2012 58
124 2 2012 50

Answer 1

OK so if I understand correctly, you want a count of rows where the TypeOfValue = 2, and the Year is in the top n values where TypeOfValue = 1, for a given Id.
This should be:
DECLARE #Id int, #NoOfRecordsToDisplay int
SET #Id = 123
SET #NoOfRecordsToDisplay = 3
SELECT COUNT(*) FROM myTable
WHERE
TypeofValue = 2
AND Id = #Id
AND [Year] IN ( SELECT TOP(#NoOfRecordsToDisplay) [Year] FROM myTable
WHERE TypeofValue = 1 AND Id = #Id
ORDER BY [Year] DESC)
In practice, you would probably want to create this as a stored proc with #Id as an input parameter. #NoOfRecordsToDisplay could either be a parameter too, or selected from some other table - I'm still not 100% clear on this from your question.
Updated SQL Fiddle here: http://sqlfiddle.com/#!3/87b0c/2
Edit: Forgot the ORDER BY on the subquery!
Edit 2: Updated query and SQL fiddle based on updated question.

Answer 2

With SQL and such these queries, understanding the problem and imagination of an algorithm or method for solving the problem is too much important, on base of what you want:
I need to get only last 3 records for targets on the basis of latest 3
values for actual
you need to have tow steps:
1.determine the last 3 years of actual values:
SELECT TOP 3 [Year]
FROM Your_Table
WHERE Typeofvalue = 1
ORDER BY [Year] DESC
2.count the records of target values which their years are in above query:
SELECT COUNT(*) FROM Your_Table
WHERE
Typeofvalue = 2
AND
[Year] IN (
SELECT TOP 3 [Year]
FROM Your_Table
WHERE Typeofvalue = 1
ORDER BY [Year] DESC)
You can do it with join too instead of subquery:
SELECT COUNT(*) FROM Your_Table t
JOIN
(
SELECT TOP 3 [Year]
FROM Your_Table
WHERE Typeofvalue = 1
ORDER BY [Year] DESC
)q
ON T.[Year]=q.[Year]
WHERE t.Typeofvalue=2

Answer 3

You can select the last three actual items and join in the corresponding target items, then count the non-null values:
select
count(Id)
from (
select top 3
t2.Id
from
TheTable t1
left join TheTable t2 on t2.Year = t1.Year and t2.TypeofValue = 2
where
t1.TypeofValue = 1
order by
t1.Year desc
) x