Question

我有这个简单的查询

select * from users where name = 'User1'

我想扩展查询的功能，无论查询返回0记录，查询都会通过其他子句获取数据。

where name = 'Default'

如果第一个子句将获取某些记录，则第二个子句将被忽略。

修改

的Oracle

Answer 1

SELECT * FROM users WHERE name = 'User1'
UNION ALL 
SELECT * FROM users WHERE name = 'Default' 
    AND NOT EXISTS (SELECT 1 FROM users WHERE name='User1')

Answer 2

 IF EXISTS (SELECT * from users where name = 'User1')
   SELECT * from users where name = 'User1';
 ELSE
   SELECT * from users where name = 'Default';

Answer 3

select top 1 * from users where name in ('User1', 'Default') order by name desc

：P

Answer 4

WITH T AS   (
        SELECT  users.*,
        RANK() OVER (ORDER BY CASE WHEN name = 'User1' THEN 0 ELSE 1 END) AS RN
        FROM    users
        WHERE   name IN ( 'Default','User1')
        )
SELECT * FROM T
WHERE   RN = 1

有条件的sql查询

4 个答案: