mysql - 识别 SQL 中匹配次数最多的列中的 ID 对

Question

我正在尝试查找使用 MySQL 的共同客户数量最多的企业对。

表格如下:

+------------+------------+ 
| BusinessID | CustomerID |
+------------+------------+
| A          |          1 |
| A          |          2 |
| A          |          3 |
| B          |          4 |
| B          |          1 |
| B          |          3 |
| B          |          2 |
| C          |          3 |
| C          |          4 |
| C          |          5 |
+------------+------------+

我希望输出是企业对和共同客户的数量，如下所示:

+-------------+-------------+------------------------+
| BusinessID  | BusinessID  | Common Customers Count |
+-------------+-------------+------------------------+
| A           | B           |                      3 |
| A           | C           |                      1 |
| B           | C           |                      2 |
+-------------+-------------+------------------------+

这是我写的查询:

SELECT a.BusinessID,b.BusinessID,COUNT(*) AS ncom
FROM (SELECT BusinessID, CustomerID FROM MYTABLE) AS a JOIN       
     (SELECT BusinessID,CustomerID FROM MYTABLE) AS b 
     ON a.BusinessID < b.BusinessID AND a.CustomerID = b.CustomerID
GROUP BY a.BusinessID, b.BusinessID
ORDER BY ncom   

问题是我的数据集大约有 5m 行，这在大型数据集上似乎效率太低。我通过限制数据在较小的数据集上测试了查询 - 处理 10k 行需要 8 秒，处理 20k 行需要 30 秒，因此该查询无法运行 5m 行。我还能如何编写查询以使其更快？

Answer 1

不要使用子查询从表中获取列，这可能会阻止它使用索引。

SELECT a.BusinessID, b.BusinessID, COUNT(*) as ncom
FROM MYTABLE AS a
JOIN MYTABLE AS b ON a.BusinessID < b.BusinessID AND a.CustomerID = b.CustomerID
GROUP BY a.BusinessID, b.BusinessID
ORDER BY ncom

此外，为表指定以下索引:

CREATE INDEX ix_cust_bus ON MYTABLE (CustomerID, BusinessID);