Question

我在函数中有一个SQL查询

SELECT  DISTINCT (product_id)
      INTO  prod
      FROM  products
     WHERE       mfg_no = 'TEL'             
                AND status = p_status

有时product_id将为null或p_status将没有数据。因为这个函数不会返回任何值。

我尝试了nvl，decode和case语句来检查product_id，但没有一个不起作用。即使product_id为null或为空，如何确保我的函数执行正常？

我试图在EXCEPTION块中返回一个值，如下所示，这也没有帮助。

EXCEPTION
    WHEN NO_DATA_FOUND
    THEN
        prod := 'NA';

编辑1

CREATE OR REPLACE FUNCTION my_function (p_status VARCHAR2)
    RETURN VARCHAR2
AS
    prod     VARCHAR2 (2000);
BEGIN
    prod := NULL;  


    SELECT  DISTINCT (product_id)
      INTO  prod
      FROM  products
     WHERE  mfg_no = 'TEL' AND status = p_status;

    RETURN prod;
EXCEPTION
    WHEN NO_DATA_FOUND
    THEN
        prod := 'N/A';
        DBMS_OUTPUT.put_line ('no data found ' || SQLERRM);
    WHEN OTHERS
    THEN
        DBMS_OUTPUT.put_line ('error ' || SQLERRM);
        prod := 'N/A';
END;

Answer 1

试试这样：

CREATE OR REPLACE FUNCTION my_function (p_status VARCHAR2)
    RETURN VARCHAR2
AS
    prod     VARCHAR2 (2000);
BEGIN
    prod := NULL;

  BEGIN
    SELECT  DISTINCT (product_id)
      INTO  prod
      FROM  products
     WHERE  mfg_no = 'TEL' AND status = p_status;

  EXCEPTION
    WHEN NO_DATA_FOUND
    THEN
        prod := 'N/A';
        DBMS_OUTPUT.put_line ('no data found ' || SQLERRM);
    WHEN OTHERS
    THEN
        DBMS_OUTPUT.put_line ('error ' || SQLERRM);
        prod := 'N/A';
  END;

  RETURN prod;

END;

要查看无记录与 null值之间的区别，请参阅this sqlfiddle demo

Answer 2

另一种解决方案，使用NVL / MAX而不是DISTINCT / Exception处理：

CREATE OR REPLACE FUNCTION my_function (p_status VARCHAR2)
    RETURN VARCHAR2
AS
    prod     VARCHAR2 (2000);
BEGIN
    SELECT  NVL(MAX(product_id), 'N/A')
      INTO  prod
      FROM  products
     WHERE  mfg_no = 'TEL' AND status = p_status;
  RETURN prod;

END;

函数返回没有任何值

2 个答案: