stored-procedures - DB2 存储过程 : Dynamically Building a Select Statement for cursor

Question

我对存储过程还很陌生。我天真地认为我可以建立一个 select 语句如下。我做不到，你们中的一些人会对我的想法咧嘴一笑。

如何做我想做的事情？

提前致谢。

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@

Answer 1

下次您需要构建一些动态 SQL 语句时试试这个。

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;

需要说明的是，SQL_STATEMENT 可以是您想要的任何名称。只要确保它在 CURSOR 声明和 PREPARE 语句中是相同的即可。