calculating values to be used later in Oracle SQL

From: William Threlfall <William.Threlfall_at_albertahealthservices.ca>
Date: Fri, 21 Feb 2014 10:10:11 -0700
Message-ID: <36800EC4761690448F1B444A1AEF44BB6A6047A0_at_EXMBXC5.crha.bewell.ca>

Question for the SQL experts ...
I need to calculate a value and then use it many times as a criterion for other selections. What is the best way to do that in Oracle SQL? For example, I need to calculate, for each patient, the date of last transplant (call it LASTTX) and then select a bunch of lab results where one of the criteria in the WHERE clause would be DATE_OF_LAB > LASTTX.

In the following example I want to select the greatest non-NULL CREAT lab result from the most recent DATE_OF_LAB where the DATE_OF_LAB is greater than the date of last transplant.

This subquery gives me the date of last transplant:

(TO_DATE((MAX(PT.DATE_OF_TRANS) OVER (PARTITION BY PT.PAT_ID ORDER BY PT.PAT_ID
    ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)), 'yyyy.mm.dd')) AS LASTTX,

However, if I try to use LASTTX in subsequent SELECT subquery statements, I get an error that it is an invalid identifier.

Is there a way to do what I want without having to use that code snippet dozens of times, as in:

(SELECT MAX(CREAT) KEEP (DENSE_RANK FIRST ORDER BY X.DATE_OF_LAB DESC, X.CREAT DESC)
    FROM PATIENT_LABS X
    WHERE X.CREAT IS NOT NULL
    AND X.PAT_ID = PD.PAT_ID
    AND X.DATE_OF_LAB > LASTTX) AS MRCREAT The nuisance way would be to re-use that code snippet over and over again, such as:

(SELECT MAX(CREAT) KEEP (DENSE_RANK FIRST ORDER BY X.DATE_OF_LAB DESC, X.CREAT DESC)
    FROM PATIENT_LABS X
    WHERE X.CREAT IS NOT NULL
    AND X.PAT_ID = PD.PAT_ID
    AND X.DATE_OF_LAB >

       (SELECT MAX(PT.DATE_OF_TRANS) OVER (PARTITION BY PT.PAT_ID ORDER BY PT.PAT_ID
        ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)
        FROM PAT_TRANSPLANT PT)

  ) AS MRCREAT I think there ought to be a way to calculate variables and use them later on, but I'm just not clueing in at the moment.

Thanks, - Bill.

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Willliam J. (Bill) Threlfall, MSc
Clinical Informatics Coordinator - OTTR
Transplant Services, University of Alberta Hospital Alberta Health Services
Aberhart Centre, Room 9221
8440 112 Street
Edmonton, AB T6G 2B7

Telephone: 780-407-6175 FAX: 780-407-8981

Alberta Health Services
www.albertahealhservices.ca

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Received on Fri Feb 21 2014 - 18:10:11 CET