DB2 Stored Procedure: Dynamically Building a Select Statement for cursor

Question

I am fairly new to stored procedures. I naively thought that I could build up a select statement as follows. I cannot, and some of you will grin with what I came up with.

How does one do what I am trying to do though?

Thanks in advance.

CREATE PROCEDURE GET_CUSTOMER_FOR_BORROWER_LETTER (


    IN APPLICATION_ID INTEGER,
    IN GET_GUARANTOR INTEGER,
    IN GET_PREFERRED_CONTACT INTEGER
    )

DYNAMIC RESULT SETS 1
READS SQL DATA

P1:BEGIN
    DECLARE selectStmt VARCHAR(800);
    DECLARE selectStmtPreferred VARCHAR(400);
    DECLARE selectStmtApplicants VARCHAR(400);
    DECLARE selectStmtGuarantor VARCHAR(400);


    DECLARE cursor1 CURSOR WITH RETURN FOR
    selectStmt -- will define this later, conditionally (babe in the woods :) )
    OPEN cursor1;


    set selectStmtPreferred = 'select "preferred applicant" as recipient_type, app.APPLICATION_ID, cust.KEY from application app, customer cust, application_detail appd where app.application_id = 407634 and app.APPLICATION_ID = appd.APPLICATION_ID  and appd.PREFERRED_CONTACT_ID = cust.KEY';

    set selectStmtApplicants = 'select "applicant" as recipient_type, app.APPLICATION_ID, cust.KEY from application app, applicant applc, customer cust where app.application_id = 407634 and applc.APPLICATION_ID = app.APPLICATION_ID and applc.CUST_ID = cust.CUST_ID';

    set selectStmtGuarantor = ' union select "guarantor" as recipient_type ,app.APPLICATION_ID, cust.KEY from application app, application_guarantor appg, customer cust where app.application_id = 407634 and appg.APPLICATION_ID = app.APPLICATION_ID and appg.CUST_ID = cust.CUST_ID';

    IF GET_PREFERRED_CONTACT = 1 THEN

        IF GET_GUARANTOR = 1 THEN 
            SET selectStmt = concat (selectStmtPreferred,selectStmtGuarantor);
        ELSE 
            SET selectStmt = selectStmtPreferred;
        END IF;
    ELSE 
        IF GET_GUARANTOR = 1 THEN 
            SET selectStmt = concat (selectStmtApplicants,selectStmtGuarantor);
        ELSE 
            SET selectStmt = selectStmtApplicants;
        END IF;
    END IF;
selectStmt = concat (selectStmtPreferred,";");


END P1@

Uh, usually you have to know what the SELECT statement is, to declare a cursor (which often means compile time, if it's not a dynamic string). And look into using PREPARE and EXECUTE, which should allow you to concatenate the strings. You should be able to un-nest your ifs. And don't use the implicit-join syntax, it's deprecated; write out your JOINs instead. — Clockwork-Muse
– Clockwork-Muse, Commented May 2, 2012 at 15:55

Rakuen42 · Accepted Answer · 2012-05-03 21:18:52Z

5

Try this out next time you need to build some dynamic SQL statements.

DECLARE SELECT_STATEMENT VARCHAR(8000);

DECLARE cursor1 CURSOR WITH RETURN FOR SQL_STATEMENT;

...build dynamic sql here...

PREPARE SQL_STATEMENT FROM SELECT_STATEMENT;

OPEN cursor1;

To be clear, SQL_STATEMENT is any name you want. Just make sure it's the same in the CURSOR declaration and the PREPARE statement.

edited May 3, 2012 at 21:18

answered May 3, 2012 at 18:24

Rakuen42

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HellishHeat · Accepted Answer · 2013-07-05 09:55:08Z

2

I solved this. It's ugly but it's solved.

P1:BEGIN

    DECLARE preferredWithGuarantor CURSOR WITH RETURN FOR
            select 'preferred applicant' as recipient_type, app.APPLICATION_ID, cust.KEY from application app, customer cust, application_detail appd where app.application_id = 407634 and app.APPLICATION_ID = appd.APPLICATION_ID  and appd.PREFERRED_CONTACT_ID = cust.KEY union select 'guarantor' as recipient_type ,app.APPLICATION_ID, cust.KEY from application app, application_guarantor appg, customer cust where app.application_id = 407634 and appg.APPLICATION_ID = app.APPLICATION_ID and appg.CUST_ID = cust.CUST_ID;

    DECLARE preferred CURSOR WITH RETURN FOR
            select 'preferred applicant' as recipient_type, app.APPLICATION_ID, cust.KEY from application app, customer cust, application_detail appd where app.application_id = 407634 and app.APPLICATION_ID = appd.APPLICATION_ID  and appd.PREFERRED_CONTACT_ID = cust.KEY;

    DECLARE applicantWithGuarantor CURSOR WITH RETURN FOR
            select 'applicant' as recipient_type, app.APPLICATION_ID, cust.KEY from application app, applicant applc, customer cust where app.application_id = 407634 and applc.APPLICATION_ID = app.APPLICATION_ID and applc.CUST_ID = cust.CUST_ID union select 'guarantor' as recipient_type ,app.APPLICATION_ID, cust.KEY from application app, application_guarantor appg, customer cust where app.application_id = 407634 and appg.APPLICATION_ID = app.APPLICATION_ID and appg.CUST_ID = cust.CUST_ID;

    DECLARE applicant CURSOR WITH RETURN FOR
            select 'applicant' as recipient_type, app.APPLICATION_ID, cust.KEY from application app, applicant applc, customer cust where app.application_id = 407634 and applc.APPLICATION_ID = app.APPLICATION_ID and applc.CUST_ID = cust.CUST_ID;


    IF GET_PREFERRED_CONTACT = 1 THEN
        IF GET_GUARANTOR = 1 THEN 
            open preferredWithGuarantor;
        ELSE 
            open preferred;
        END IF;
    ELSE 
        IF GET_GUARANTOR = 1 THEN 
            open applicantWithGuarantor;
        ELSE
            open applicant;
        END IF;
    END IF;

END P1@

edited Jul 5, 2013 at 9:55

answered May 2, 2012 at 13:50

HellishHeat

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2 Comments

Ian Bjorhovde Over a year ago

This may be ugly, but it is certainly a lot easier to read and maintain than dynamically building the SQL statement in code.

huahsin68 Over a year ago

Well done, although it is urgly but you have minimize the risk of SQL injection.

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