你可以从 balance2 使用 UNION 添加数据的步骤 balance 在中不可用 balance2 .

SELECT ID, balance FROM balance2
UNION
SELECT b.ID, b.balance FROM balance b
LEFT JOIN balance2 b2 ON b2.ID = b.ID
WHERE b2.ID IS NULL
ORDER BY ID

输出：

| ID | balance |
|----|---------|
|  1 |      12 |
|  2 |     7.5 |
|  3 |       0 |
|  4 |    2.33 |
| 10 |    1.23 |

看到这把小提琴了吗

我有另一个主意。我们可以把第二张table留给第一张。然后把第一个表和第二个表连接起来。把他们两个联合起来以得到结果。

select id,balance
from ((select b2.id as 'id',b2.balance as 'balance'
from balance2 b2
LEFT JOIN balance b 
ON b2.id = b.id)
UNION
(select b.id as 'id',IF(b2.balance is null,b.balance,b2.balance) as 'balance'
from balance b 
LEFT JOIN balance2 b2
ON b.id = b2.id)) derived_table
order by id;