Mysql 如何连接两个表并匹配空值

我有这些桌子：

mysql> select bookId, productId, clusterId, symbolId, shares from SymbolAimOrderStats where bookId = "BFM";
+--------+-----------+-----------+----------+--------+
| bookId | productId | clusterId | symbolId | shares |
+--------+-----------+-----------+----------+--------+
| BFM    | NULL      | NULL      | NULL     |    522 |
| BFM    | BFM       | NULL      | NULL     |    522 | 
| BFM    | BFM       | BFM       | NULL     |    522 | 
| BFM    | BFM       | BFM       | 0000f52a |    506 | 
| BFM    | BFM       | BFM       | 00010a4d |      2 | 
| BFM    | BFM       | BFM       | 00010a7c |      1 | 
| BFM    | BFM       | BFM       | 00010a89 |      3 | 
| BFM    | BFM       | BFM       | 00010ba3 |      3 | 
| BFM    | BFM       | BFM       | 00013c7e |      3 | 
| BFM    | BFM       | BFM       | 00013c97 |      4 | 
+--------+-----------+-----------+----------+--------+
10 rows in set (0.00 sec)

mysql> select bookId, productId, clusterId, symbolId, shares from SymbolOrderStats where bookId = "BFM";
+--------+-----------+-----------+----------+--------+
| bookId | productId | clusterId | symbolId | shares |
+--------+-----------+-----------+----------+--------+
| BFM    | NULL      | NULL      | NULL     |    393 | 
| BFM    | BFM       | NULL      | NULL     |    393 | 
| BFM    | BFM       | BFM       | NULL     |    393 | 
| BFM    | BFM       | BFM       | 0000f52a |    377 | 
| BFM    | BFM       | BFM       | 00010a4d |      2 | 
| BFM    | BFM       | BFM       | 00010a7c |      1 | 
| BFM    | BFM       | BFM       | 00010a89 |      3 | 
| BFM    | BFM       | BFM       | 00010ba3 |      3 | 
| BFM    | BFM       | BFM       | 00013c7e |      3 | 
| BFM    | BFM       | BFM       | 00013c97 |      4 | 
+--------+-----------+-----------+----------+--------+
10 rows in set (0.00 sec)

我想联接这些表并从这两个表中获取shares列，包括具有空值的行

我知道你不能匹配空值，所以这当然不能给出我想要的结果：

mysql> select a.bookId, a.productId, a.clusterId, a.symbolId, a.shares, o.shares 
from SymbolAimOrderStats a 
left join SymbolOrderStats o 
on a.bookId = o.bookId and a.productId = o.productId and 
a.clusterId = o.clusterId and a.symbolId = o.symbolId where a.bookId = "BFM";

所以我试过这个：

mysql> select a.bookId, a.productId, a.clusterId, a.symbolId, a.shares, o.shares 
from SymbolAimOrderStats a 
left join SymbolOrderStats o 
on a.bookId = o.bookId and 
(a.productId = o.productId or (a.productId is null and o.productId is null)) and 
(a.clusterId = o.clusterId or (a.clusterId is null and o.clusterId is null)) and
(a.symbolId = o.symbolId or (a.symbolId is null or a.symbolId is null)) 
where a.bookId = "BFM";

但这也不能满足我的需求。有人能告诉我怎样才能得到我想要的结果集吗

这是我想要的回报：

+--------+-----------+-----------+----------+--------+--------+
| bookId | productId | clusterId | symbolId | shares | shares |
+--------+-----------+-----------+----------+--------+--------+
| BFM    | NULL      | NULL      | NULL     |    522 |    393 |
| BFM    | BFM       | NULL      | NULL     |    522 |    393 | 
| BFM    | BFM       | BFM       | NULL     |    522 |    393 | 
| BFM    | BFM       | BFM       | 0000f52a |    506 |    377 | 
| BFM    | BFM       | BFM       | 00010a4d |      2 |      2 | 
| BFM    | BFM       | BFM       | 00010a7c |      1 |      1 | 
| BFM    | BFM       | BFM       | 00010a89 |      3 |      3 | 
| BFM    | BFM       | BFM       | 00010ba3 |      3 |      3 | 
| BFM    | BFM       | BFM       | 00013c7e |      3 |      3 | 
| BFM    | BFM       | BFM       | 00013c97 |      4 |      4 | 
+--------+-----------+-----------+----------+--------+--------+
10 rows in set (0.00 sec)

---

这是在MySQL中。

可能

NULL

值的最后一个条件应该使用

和
而不是
或
：

select a.bookId, a.productId, a.clusterId, a.symbolId, a.shares, o.shares 
from SymbolAimOrderStats a 
left join SymbolOrderStats o 
on a.bookId = o.bookId and 
(a.productId = o.productId or (a.productId is null and o.productId is null)) and 
(a.clusterId = o.clusterId or (a.clusterId is null and o.clusterId is null)) and
(a.symbolId = o.symbolId or (a.symbolId is null and o.symbolId is null)) 
------------------------------------------------^ --^
where a.bookId = "BFM";

如果需要有意义的
NULL
，请将其更改为有意义的内容

select  a.bookId, a.productId, a.clusterId, a.symbolId, a.shares, o.shares 
from    SymbolAimOrderStats a 
left join SymbolOrderStats o 
  on    a.bookId = o.bookId
   and ifnull( a.productId, @dummy ) = ifnull( o.productId, @dummy )
   and ifnull( a.clusterId, @dummy ) = ifnull( o.clusterId, @dummy )
   and ifnull( a.symbolId, @dummy ) = ifnull( o.symbolId, @dummy ) 
where a.bookId = "BFM";

其中，
@dummy
是任何值，只要它不与非空值冲突，以消除将
null
与非
null
匹配的可能性，并且是与字段相同的数据类型。如果productId、clusterId和symbolId是不同的类型，则需要三个伪变量。或者您可以在那里硬编码值，但这不是一个好的做法

然而，这就提出了一个问题：如果表中的
NULL
值实际上意味着什么，为什么它们还没有设置为这些值？我并不想批评——可能有完全合理的理由让它们保持
NULL
。但是，您可能忽略了改进数据的机会。
您还没有向我们展示您的需求。请发布期望的结果。对不起，我认为这是清楚的。我已经用这些信息更新了我的问题。而且它应该是o.symbol，在和你们两个-2个愚蠢的打字错误之后。数据是通过使用汇总选择的查询创建的。空值是所有符号、簇和符号或产品、簇和符号的集合。是的，创建数据的代码可以将空值更改为其他内容，但是有很多现有代码期望空值指示聚合。