SQL query with multiple time based criteria - sql

Question

I have a database for managing blood lead levels where we have various reporting/exclusion requirements.
For mandatory removal of someone from my area they need a test over 34, and before they are allowed to return they require 3 consecutive tests to be under 27. I have been using the query below to find people that should be removed this looks at their last 3 tests for any over 34, This works to say a person must be excluded based on their last 3 tests, but does not work to generate a complete list of people that should currently be excluded
SELECT x1.[Employee ID]
FROM [Lead Results] AS x1 INNER JOIN Employees ON x1.[Employee ID] = Employees.[Employee ID]
WHERE (((x1.[Test Result])>34) AND (((select count(*)
from [Lead Results] x2
where x2.[Employee ID] = x1.[Employee ID]
and x2.[Date of Test] >= x1.[Date of Test]
))<=3))
GROUP BY x1.[Employee ID]
HAVING ((Count(x1.[Date of Test]))>=1);
I have also made a query to find people that have their last 3 tests under 27, This works fine to say someone can now be returned,
SELECT x1.[Employee ID]
FROM [Lead Results] AS x1 INNER JOIN Employees ON x1.[Employee ID] = Employees.[Employee ID]
WHERE (((x1.[Test Result])<27) AND (((select count(*)
from [Lead Results] x2
where x2.[Employee ID] = x1.[Employee ID]
and x2.[Date of Test] >= x1.[Date of Test]
))<=3))
GROUP BY x1.[Employee ID], Employees.[Current Employee]
HAVING ((Count(x1.[Date of Test]))>=3);
obviously these two queries work but only for the last 3 tests.
How can I get all the employee ids for people that have tested over 34, but have not yet had 3 consecutive tests under 27 since their high result.

Answer 1

Start with the most recent date where you have a test of 34:
select [Employee ID], max([Date of Test]) as max34
from [Lead Results]
where [Test Result] > 34
group by [Employee ID];
Next, calculate the most recent date where there are three tests all below 27. This is a bit harder, but it can be done.
The following actually finds tests where the previous, next, and current are all less than 27. It then aggregates these to get the latest value.
select [Employee ID], max([Date of Test]) as MiddleTest27
from [Lead Results] as lr
where [Test Result] < 27 and
(select top 1 [Test Result]
from [Lead Results] as lr2
where lr2.[Employee ID] = lr.[Employee ID] and lr2.[Date of Test] < lr.[Date of Test]
order by [Date of Test] desc, id desc
) < 27 and
(select top 1 [Test Result]
from [Lead Results] as lr2
where lr2.[Employee ID] = lr.[Employee ID] and lr2.[Date of Test] > lr.[Date of Test]
order by [Date of Test] asc, id asc
) < 27
group by [Employee ID]
Next, we can combine these to get what you want: Employees whose most recent test is in the first query but not the second:
select e34.*
from (select [Employee ID], max([Date of Test]) as max34
from [Lead Results]
where [Test Result] > 34
group by [Employee ID]
) as e34 left join
(select [Employee ID], max([Date of Test]) as MiddleTest27
from [Lead Results] as lr
where [Test Result] < 27 and
(select top 1 [Test Result]
from [Lead Results] as lr2
where lr2.[Employee ID] = lr.[Employee ID] and lr2.[Date of Test] < lr.[Date of Test]
order by [Date of Test] desc, id desc
) < 27 and
(select top 1 [Test Result]
from [Lead Results] as lr2
where lr2.[Employee ID] = lr.[Employee ID] and lr2.[Date of Test] > lr.[Date of Test]
order by [Date of Test] asc, id asc
) < 27
group by [Employee ID]
) as e27
on e34.[Employee ID] = e27.[Employee ID]
where e27.[Employee ID] is NULL or e27.MiddleTest27 < e34.max34
That is, there is either no more recent "27" sequence or the last one predated the "34" sequence.