ORACLE使用CASE WHEN的方法

先寫草稿。

說下我的需求，ORACLE數據庫有兩個字段RECEIVER_MOBILE與RECEIVER_PHONE，同為聯系方式。當RECEIVER_MOBILE為空的時候，需要用到RECEIVER_PHONE，但是查詢語句字段不能多於，於是有了下面的語句。

SELECT RECEIVER_MOBILE,RECEIVER_PHONE,CASE WHEN RECEIVER_MOBILE IS NULL THEN (SELECT TO_CHAR(RECEIVER_PHONE) FROM TB_EXT_TRADE WHERE TID LIKE '%DH1504103135-095%')
 ELSE '' END AS mobile from TB_EXT_TRADE WHERE TID like '%DH1504103135-095%';
期間，遇到一些問題，詳細再說。