存储过程 - 表列名作为变量

Question

我这里有一个存储过程，它从示例数据库中调用表列，但我的问题是我想将一个列名变成一个变量，以便我可以在某个条件下使用它。我的代码不起作用，但我不知道如何将其作为变量。

我想将列名 SALARY 作为变量。

这是我的代码：

CREATE PROCEDURE TAXEXEMPT ()

    DYNAMIC RESULT SETS 1
    LANGUAGE SQL

BEGIN

    DECLARE display CURSOR WITH RETURN TO CLIENT FOR

        SELECT EMPNO, LASTNAME, SALARY, SALARY AS "TAX EXEMPTION" 
        FROM EMPLOYEE 
        WHERE WORKDEPT BETWEEN 'C01' AND 'D21';

        IF ( SALARY < 15001 ) THEN
            --DO NOTHING
        ELSEIF ( SALARY >= 15001 OR SALARY <= 22000 ) THEN
            UPDATE EMPLOYEE SET "TAX EXEMPTION" = SALARY * 1.03;
        ELSEIF ( SALARY >= 22001 OR SALARY <= 32000 ) THEN
            UPDATE EMPLOYEE SET "TAX EXEMPTION" = (SALARY * 1.05) + 100;
        ELSEIF ( SALARY >= 32001 OR SALARY <= 45000 ) THEN
            UPDATE EMPLOYEE SET "TAX EXEMPTION" = (SALARY * 1.07) + 200;
        ELSE
            --DO NOTHING
        END IF; 

    OPEN display;

END

任何形式的帮助都可以，在此先感谢。

Answer 1

你想要的是一个 CASE 表达式：

DECLARE display CURSOR WITH RETURN TO CLIENT FOR

         SELECT EMPNO, LASTNAME, SALARY, 
                   CASE 
                     WHEN SALARY < 15001 THEN SALARY 
                     WHEN SALARY BETWEEN 15001 AND <= 22000 THEN SALARY * 1.03
                     WHEN SALARY BETWEEN 20001 AND <= 32000 THEN (SALARY * 1.05) + 100
                     ...
                     ELSE SALARY
                   END AS "TAX EXEMPTION" 
         FROM EMPLOYEE 
         WHERE WORKDEPT BETWEEN 'C01' AND 'D21';

     OPEN display;