在 Oracle 中处理异常

Question

我正在尝试将输入的年份解析为字符串（请不要让我开始 - 它就是这样）。但是，有些年份输入无法被 TO_NUMBER 解析。

WITH src AS (
        SELECT '2000' AS y FROM DUAL
  UNION SELECT '1991' AS y FROM DUAL
  UNION SELECT '20--' AS y FROM DUAL
  UNION SELECT '09' AS y FROM DUAL
  UNION SELECT '11' AS y FROM DUAL
  UNION SELECT '95' AS y FROM DUAL
)

BEGIN
  SELECT
    s.y,
    TO_NUMBER(s.y) AS p
  FROM src s
EXCEPTION
  WHEN INVALID_NUMBER THEN NULL
END

我从未在 Oracle 中进行过异常处理，如果这是一个如此基本的问题，我深表歉意。

在上面运行我的查询时，我得到ORA-00928: missing SELECT keyword，然后它突出显示BEGIN 关键字。通过搜索，我看到人们所做的就是使用BEGIN SELECT，这也是我正在做的事情。我猜我在其他地方搞砸了？

基本上我想做的是解析字符串，如果抛出异常，我会将其设置为NULL。

编辑

我尝试了一种不同的方法并添加了一些分号，正如@DavidFaber 在下面评论的那样。

BEGIN
  SELECT
    s.y,
    TO_NUMBER(s.y) AS p
  FROM (
          SELECT '2000' AS y FROM DUAL
    UNION SELECT '1991' AS y FROM DUAL
    UNION SELECT '20--' AS y FROM DUAL
    UNION SELECT '09' AS y FROM DUAL
    UNION SELECT '11' AS y FROM DUAL
    UNION SELECT '95' AS y FROM DUAL
  ) s;
EXCEPTION
  WHEN INVALID_NUMBER THEN NULL;
END;

我现在收到另一个错误ORA-06550: line 2, column 3: PLS-00428: an INTO clause is expected in this SELECT statement。

Answer 1

There's no exception-handling in SQL;

是的，没错，但是有像内联函数（Oracle 12c）这样的解决方法：

WITH FUNCTION safe_to_NUMBER(input IN VARCHAR2)
RETURN NUMBER IS
i NUMBER;
BEGIN
  i:= TO_NUMBER(input);

  RETURN i;
  EXCEPTION
  WHEN OTHERS THEN 
    RETURN NULL;
END;
SELECT  sub.y, safe_to_NUMBER(sub.y)
FROM (
    SELECT '2000' AS y FROM DUAL UNION ALL
    SELECT '1991' AS y FROM DUAL UNION ALL
    SELECT '20--' AS y FROM DUAL UNION ALL
    SELECT '09' AS y FROM DUAL UNION ALL
    SELECT '11' AS y FROM DUAL UNION ALL
    SELECT '95' AS y FROM DUAL
  ) sub;

结果：

Y    SAFE_TO_NUMBER(SUB.Y)
---- ---------------------
2000                  2000
1991                  1991
20--                      
09                       9
11                      11
95                      95

6 rows selected. 

我当然不会写这样的生产代码:)

---

正确方式（DEFAULT NULL ON CONVERSION ERROR - 从 Oracle12cR2 开始可用）：

SELECT sub.y, TO_NUMBER(sub.y DEFAULT NULL ON CONVERSION ERROR) AS y
FROM (
    SELECT '2000' AS y FROM DUAL UNION ALL
    SELECT '1991' AS y FROM DUAL UNION ALL
    SELECT '20--' AS y FROM DUAL UNION ALL
    SELECT '09' AS y FROM DUAL UNION ALL
    SELECT '11' AS y FROM DUAL UNION ALL
    SELECT '95' AS y FROM DUAL
  ) sub;

输出：

Y             Y
---- ----------
2000       2000
1991       1991
20--           
09            9
11           11
95           95

6 rows selected. 

Answer 2

SQL 中没有异常处理；您需要创建一个 PL/SQL 块来处理异常（请注意，我将您的 UNIONs 更改为 UNION ALL）：

BEGIN
  WITH src AS (
    SELECT '2000' AS y FROM DUAL UNION ALL
    SELECT '1991' AS y FROM DUAL UNION ALL
    SELECT '20--' AS y FROM DUAL UNION ALL
    SELECT '09' AS y FROM DUAL UNION ALL
    SELECT '11' AS y FROM DUAL UNION ALL
    SELECT '95' AS y FROM DUAL
  )
  SELECT s.y, TO_NUMBER(s.y) AS p
    FROM src s;
EXCEPTION
  WHEN INVALID_NUMBER THEN NULL;
END;
/

但您可以使用正则表达式来执行“安全”数字转换，而不是使用 PL/SQL 块：

  WITH src AS (
    SELECT '2000' AS y FROM DUAL UNION ALL
    SELECT '1991' AS y FROM DUAL UNION ALL
    SELECT '20--' AS y FROM DUAL UNION ALL
    SELECT '09' AS y FROM DUAL UNION ALL
    SELECT '11' AS y FROM DUAL UNION ALL
    SELECT '95' AS y FROM DUAL
  )
  SELECT s.y, TO_NUMBER(REGEXP_SUBSTR(s.y, '^\d+'))
    FROM src s;

上面会将值 20-- 转换为 20，这可能不是您想要的 - 在这种情况下，请尝试使用此模式 ^\d+$：

  WITH src AS (
    SELECT '2000' AS y FROM DUAL UNION ALL
    SELECT '1991' AS y FROM DUAL UNION ALL
    SELECT '20--' AS y FROM DUAL UNION ALL
    SELECT '09' AS y FROM DUAL UNION ALL
    SELECT '11' AS y FROM DUAL UNION ALL
    SELECT '95' AS y FROM DUAL
  )
  SELECT s.y, TO_NUMBER(REGEXP_SUBSTR(s.y, '^\d+$'))
    FROM src s;

希望这会有所帮助。