MySQL中的两步左连接

我正试着左键连接两张桌子。表1（tb1）如下所示：

表2（tb2）如下所示：

我想首先使用

ID

左键连接两个表。对于表2中

ID

为空的记录，我想使用

name

作为键

我知道我可以先在

tb1.ID=tb2.ID

和

tb1.DATE

上加入表1， 使用方法

createtable my_table选择as

creatinganewtable，然后为新表再次执行左连接。问题是我在表1和表2中有数千条记录。即使当我试图使用

ID

为第一个连接创建一个新表时，SQL Workbench也会给我一个错误代码，表示连接丢失

---

create view my_view

将解决连接问题。但我想知道我如何才能做到两步连接的观点？提前谢谢。

你在找这样的东西吗

SELECT *
  FROM table1 t1 LEFT JOIN table2 t2
    ON t1.date = t2.date
   AND (t1.id = t2.id OR (t1.id IS NULL AND t1.name = t2.name));

样本输出：

+------------+------+--------+------------+------+--------+-------+
| DATE       | ID   | NAME   | DATE       | ID   | NAME   | Sales |
+------------+------+--------+------------+------+--------+-------+
| 2007-09-01 | 1    | Apple  | 2007-09-01 |    1 | Apple  |   200 |
| 2007-10-01 | 2    | Pear   | 2007-10-01 |    2 | Pear   |   100 |
| 2007-11-01 | 3    | Banana | 2007-11-01 |    3 | Banana |   300 |
| 2007-12-01 | NULL | Cherry | 2007-12-01 |    4 | Cherry |   500 |
| 2008-01-01 | 11   | Kiwi   | NULL       | NULL | NULL   |  NULL |
+------------+------+--------+------------+------+--------+-------+

---

下面是一个演示

发布您的sqlquery@Strawberry想解释一下吗？不，我错了，谢谢。这正是我想要的。

SELECT *
  FROM table1 t1 LEFT JOIN table2 t2
    ON t1.date = t2.date
   AND (t1.id = t2.id OR (t1.id IS NULL AND t1.name = t2.name));

+------------+------+--------+------------+------+--------+-------+
| DATE       | ID   | NAME   | DATE       | ID   | NAME   | Sales |
+------------+------+--------+------------+------+--------+-------+
| 2007-09-01 | 1    | Apple  | 2007-09-01 |    1 | Apple  |   200 |
| 2007-10-01 | 2    | Pear   | 2007-10-01 |    2 | Pear   |   100 |
| 2007-11-01 | 3    | Banana | 2007-11-01 |    3 | Banana |   300 |
| 2007-12-01 | NULL | Cherry | 2007-12-01 |    4 | Cherry |   500 |
| 2008-01-01 | 11   | Kiwi   | NULL       | NULL | NULL   |  NULL |
+------------+------+--------+------------+------+--------+-------+