mysql - 这个场景需要一个sql查询

Question

大家好，请帮我为该场景连接一个 sql 查询

表

+----+---------+--------+------------+--------------+
| ID | country | region | restaurant | locationcode |
+----+---------+--------+------------+--------------+
|  1 | IND     | DL     | xyz        |          100 |
|  2 | IND     | DL     | yzc        |          111 |
+----+---------+--------+------------+--------------+

选择所有项目 ---

if condition matched with country,region,restaurant,locationcode
  If not then all items that matched condition with country,region,restaurant
      if not then all items that matched the condition with country,region

我可以使用 sql 查询来做到这一点，还是必须使用应用程序逻辑来处理它？<​​/p>

Answer 1

这个解决方案有点冗长，但应该可行。使用 CASE 从选项中进行选择，并使用这些行的存在作为选择条件。

SELECT id FROM mytable WHERE 
CASE 
     WHEN EXISTS( SELECT 1 FROM mytable WHERE region='DL' AND country='IND'
                   AND restaurant='xyz' AND locationcode='100')
       THEN region='DL' AND country='IND' AND restaurant='xyz' AND locationcode='100'
     WHEN EXISTS( SELECT 1 FROM mytable WHERE region='DL' AND country='IND')
       THEN region='DL' AND country='IND'
     WHEN EXISTS( SELECT 1 FROM mytable WHERE region='DL' )
       THEN region = 'DL';
     END;