Question

Below is the simplified version of the Table.
My query is select all the patientIds where the last X Test Result is over10. Result should be only patientID 1 and 3.

There are over 30k records in this table. I couldn’t figure out a better way to get this done.

PatientId   Test    Result  Date
1           X       11      2011/05/11
1           X        5      2005/05/11
1           Y        5      2011/05/11
2           X        5      2011/05/11
2           X       12      2005/05/11
2           Z       12      2011/05/11
3           X       16      2011/05/11
4           X       9       2005/05/11

Answer 1

I would do something like this:

SELECT a.PatientId
FROM
    some_table AS a
    INNER JOIN (
        SELECT PatientId, MAX(Date) AS Date
        FROM some_table
        WHERE Test = 'X'
        GROUP BY PatientId
    ) AS lr ON a.PatientId = lr.PatientId AND a.Date = lr.Date
WHERE a.Test = 'X' AND a.Result > 10