Sql 在日期相同或过去的第一个id上加入

只有当表1的日期回答了问题的原始版本时，我才能将表1加入到opid的表2中

我想你想要一个完整的加入：

select t1.id, t1.date, t1.spend, t2.id as table2_id, t2.users
from table1 t1 full join
     table2 t2
     on t1.date = t2.date;

---

我想你应该试试内部连接

选择t1.id、t1.date、t1.expense、t2.id作为表2\u id、t2.users
来自表1 t1内部联接
表2 t2
在t1.date，表2在表1的最新（日期）行与相同的
id2
连接，但不一定相同。
+------------+-------+-----+
| date       | users | opid|
+------------+-------+-----+
| 2019-07-06 | 100   |  1  |
+------------+-------+-----+
| 2019-07-08 | 200   |  2  | 
+------------+-------+-----+ 

+------------+-------+-------+
| date       | spend | users |
+------------+-------+-------+
| 2019-07-05 | 10    | 100   |
+------------+-------+-------+
| 2019-07-07 | 4     | null  |
+------------+-------+-------+
| 2019-07-08 | 6     | 200   |
+------------+-------+-------+  

select t1.id, t1.date, t1.spend, t2.id as table2_id, t2.users
from table1 t1 full join
     table2 t2
     on t1.date = t2.date;