如何使用Oracle中的SQL中的REGEXP_SUBSTR将自定义消息替换为空插槽

Posted 2021-04-04

我有一个任务，我有一个“供应商”表，每个供应商都有一个描述。某些描述提供了电子邮件地址，而其他描述则没有。我需要显示提供的电子邮件，如果没有，我需要显示“没有提供电子邮件”。我很容易提取电子邮件地址，但我无法弄清楚如何用所请求的消息替换所有空插槽。

我尝试了几种，可能是非常错误的方法：

尝试1：

SELECT REGEXP_SUBSTR(description, '[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+.[A-Za-z]{2,4}') OR 'No email provided' "Supplier emails" FROM suppliers;

尝试2 :(注意：我预计这不能正常工作但是由于缺乏其他想法而决定试一试）

SELECT REGEXP_SUBSTR(description, '[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+.[A-Za-z]{2,4}') || 'No email provided' "Supplier emails" FROM suppliers;

尝试3：

SELECT REGEXP_SUBSTR(description, '[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+.[A-Za-z]{2,4}', 'No email provided') "Supplier emails" FROM suppliers;

尝试4：

SELECT REGEXP_SUBSTR(description, '[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+.[A-Za-z]{2,4}') "Supplier emails" FROM suppliers;
SELECT REPLACE('-', "No Email Provided") FROM suppliers;

我试着在谷歌上查看这个措辞的变化，而我的教科书并没有清楚地解释这个具体情况。

这是我正在使用的表，关于结果的上下文：

INSERT INTO suppliers
  VALUES ('Second Hand Reads', 
         'wholesaler of used books only, located in Chicago, 634.555-8787');
INSERT INTO suppliers
  VALUES ('Leftovers', 
     'Physical store location, located in Seattle, willing to fill referred sales, [e-mail]');
INSERT INTO suppliers
  VALUES ('Read Again', 
 'Chain of used book store fronts, seeking online sales partner, located in western U.S., 919-555-3333');
INSERT INTO suppliers
  VALUES ('Bind Savers', 'Used book wholsaler, stock includes international titles, 402-555-2323');
INSERT INTO suppliers
  VALUES ('Book Recyclers', 'Used book chain, located in Canada, large volume of sales, 888.555.5204');
INSERT INTO suppliers
  VALUES ('Page Shock', 'Book wholsaler for specialty books and graphic novels, [e-mail]');
INSERT INTO suppliers
  VALUES ('RePage', 'Used book vendor, only wholesales, Wash D.C., 555-0122');
COMMIT;

预期的产出是

                           Supplier emails
------------------------------------------------------------------
No email provided
--------------------
[e-mail]
--------------------
No email provided
--------------------
No email provided
--------------------
No email provided
--------------------
[e-mail]
--------------------
No email provided

但是输出要么是错误，要么是我预期的不起作用

                           Supplier emails
------------------------------------------------------------------
No email provided
-------------------------------------
[e-mail] email provided
-------------------------------------
No email provided
-------------------------------------
No email provided
-------------------------------------
No email provided
-------------------------------------
[e-mail] email provided
-------------------------------------
No email provided

答案

你需要使用NVL或COALESCE函数：

SELECT STORE_NAME,
       DESCRIPTION,
       NVL(REGEXP_SUBSTR(description, '[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+.[A-Za-z]{2,4}'),
           'No email provided') AS EMAIL
  FROM SUPPLIERS

dbfiddle here

NVL接受两个论点。如果第一个参数不是NULL，则返回它;否则它返回第二个参数。

COALESCE类似于NVL，但它接受尽可能多的参数，因为你需要提供并返回第一个非NULL的参数。如果所有参数都为NULL，则COALESCE将返回NULL。

祝你好运。