I wish I could correlate an "inline view"

Question

I have a Patient table:

PatientId   Admitted
---------   ---------------
1           d/m/yy hh:mm:ss
2           d/m/yy hh:mm:ss
3           d/m/yy hh:mm:ss

I have a PatientMeasurement table (0 to many):

PatientId   MeasurementId   Recorded            Value
---------   -------------   ---------------     -----
1           A               d/h/yy hh:mm:ss     100
1           A               d/h/yy hh:mm:ss     200
1           A               d/h/yy hh:mm:ss     300
2           A               d/h/yy hh:mm:ss     10
2           A               d/h/yy hh:mm:ss     20
1           B               d/h/yy hh:mm:ss     1
1           B               d/h/yy hh:mm:ss     2

I am trying to create a result set that resembles:

PatientId   Numerator   Denominator
---------   --------    -----------
1           1           1
2           1           1
3           0           1       

Essentially, a patient will have a 1 in the numerator if the have at least one value for measurement A and one value for measurement B. In this example, patient 1 has 3 A measurements and 2 B measures, so the numerator is 1. Patient 2 has 2 A measurements, but no B measurements, so the numerator is 0. Patient has neither an A measurement nor a B measurement, so the numerator is 0.

My query thus far is:

SELECT  PatientId, CASE WHEN a.cnt+b.cnt>2 THEN 1 ELSE 0 END Numerator, 1 Denominator
FROM    patient p

LEFT OUTER JOIN (
    SELECT  PatientId, count(*) cnt
    FROM    PatientMeasurement pm
    WHERE   MeasurementId='A'
    --AND   Recorded <= dateadd(hh, 12, Admitted)
    GROUP BY PatientId
) a ON p.PatientId=a.PatientId

LEFT OUTER JOIN (
    SELECT  PatientId, count(*) cnt
    FROM    PatientMeasurement pm
    WHERE   MeasurementId='B'
    --AND   Recorded <= dateadd(hh, 12, Admitted)
    GROUP BY PatientId
) b ON p.PatientId=b.PatientId

This works as expected as long as I don't include the correlated, date restriction (Recorded < dateadd(hh, 12, Admitted). Unfortunately, correlating an 'inline view' in this manner is not syntactically valid.

This has forced me to re-write the SQL to:

SELECT  PatientId, CASE WHEN v.a+v.b>2 THEN 1 ELSE 0 END Numerator, 1 Denominator
FROM    (

    SELECT  PatientId,
    (
        SELECT  PatientId, count(*) cnt
        FROM    PatientMeasurement pm
        WHERE   PatientId=p.PatientId
        AND MeasurementId='A'
        AND Recorded <= dateadd(hh, 12, Admitted)
        GROUP BY PatientId
    ) a,
    (
        SELECT  PatientId, count(*) cnt
        FROM    PatientMeasurement pm
        WHERE   PatientId=p.PatientId
        AND MeasurementId='B'
        AND Recorded <= dateadd(hh, 12, Admitted)
        GROUP BY PatientId
    ) b
    FROM    Patient p
) v

My question: Is there a better, more-efficient way to do this?

Thanks for your time.

Answer 1

Try this :

WITH GroupPatients AS 
    (SELECT MeasurementID, PatientId, Count(*) AS cnt
    FROM PatientMeasurement AS pm
    INNER JOIN Patient p ON pm.PatientID = p.PatientID
    WHERE
        MeasurementId IN ('A', 'B')
    AND
        Recorded <= dateadd(hh, 12, Admitted)
    GROUP BY MeasureMentID, PatientId)

SELECT p.PatientID, Case
    When IsNull(GPA.cnt, 0) > 0 AND IsNull(GPB.cnt, 0) > 0 Then 1
    Else 0
End AS Numerator, 1 AS Denominator
FROM Patient p
LEFT JOIN GroupPatientsA AS GPA ON p.PatientID = GPA.PatientID AND GPA.MeasurementID = 'A'
LEFT JOIN GroupPatientsB AS GPB ON p.PatientID = GPB.PatientID AND GPB.MeasurementID = 'B'

I've made one tweak to the business logic too - your spec says Numerator should be one if a patient has both A and B measurements - however, your clause of a.cnt+b.cnt>2 will erroneously return one if either a.cnt or b.cnt are 3 or more and the other is zero.