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mysql - 在单个外部 SELECT 查询中使用来自 SELECT 子查询的两个聚合值

问题描述

对于相关的表和列（比以下更多），我有一个customer带有cust_id和state 列的account表和一个带有account_id、cust_id和avail_balance列的表。

示例customer表：

| cust_id | state |
|--------:|-------|
|       1 | MA    |
|       2 | MA    |
|       3 | MA    |
|       4 | MA    |
|       5 | NH    |
|       6 | MA    |
|       7 | MA    |
|       8 | NH    |
|       9 | MA    |
|      10 | NH    |
|      11 | MA    |
|      12 | NH    |
|      13 | MA    |

示例account表：

| account_id | cust_id | avail_balance |
|-----------:|--------:|--------------:|
|          1 |       1 |       1057.75 |
|          2 |       1 |           500 |
|          3 |       1 |          3000 |
|          4 |       2 |       2258.02 |
|          5 |       2 |           200 |
|          7 |       3 |       1057.75 |
|          8 |       3 |        2212.5 |
|         10 |       4 |        534.12 |
|         11 |       4 |        767.77 |
|         12 |       4 |       5487.09 |
|         13 |       5 |       2237.97 |
|         14 |       6 |        122.37 |
|         15 |       6 |         10000 |
|         17 |       7 |          5000 |
|         18 |       8 |       3487.19 |
|         19 |       8 |        387.99 |
|         21 |       9 |        125.67 |
|         22 |       9 |       9345.55 |
|         23 |       9 |          1500 |
|         24 |      10 |      23575.12 |
|         25 |      10 |             0 |
|         27 |      11 |       9345.55 |
|         28 |      12 |      38552.05 |
|         29 |      13 |         50000 |

这是我希望优化的查询示例。

SELECT account.cust_id
FROM account, customer
WHERE
      account.cust_id = customer.cust_id
  AND customer.state = 'MA'
  AND customer.cust_id >
      (SELECT MAX(customer.cust_id) AS max_nh_cust_id
       FROM account, customer
       WHERE
             account.cust_id = customer.cust_id
         AND state = 'NH')
  AND account.avail_balance >
      (SELECT MAX(avail_balance) AS max_nh_avail_balance
       FROM account, customer
       WHERE
             account.cust_id = customer.cust_id
         AND state = 'NH');

上述示例数据的预期结果（如果数据不同，可能不仅仅是 1 个结果）：

| cust_id |
|--------:|
|      13 |

account上面的问题是代码冗余以及我们如何使用两个子查询多次遍历表。我希望可以使用一个子查询从表中获取最大值cust_id，并在外部查询中使用这两个标量。例如，查询的形状可能如下所示：avail_balanceaccount

SELECT account.cust_id
FROM account, customer
WHERE
      account.cust_id = customer.cust_id
  AND (customer.cust_id > max_nh_cust_id AND account.avail_balance) > max_nh_avail_balance) IN
      (SELECT MAX(customer.cust_id) AS max_nh_cust_id, MAX(avail_balance) AS max_nh_avail_balance
       FROM account, customer
       WHERE
             account.cust_id = customer.cust_id
         AND state = 'NH');

显然，上面的方法是行不通的。实现上述代码冗余较少且仅在一个查询中（可能包含子查询）的最有效方法是什么？

标签： mysqlselectsubqueryquery-optimizationaggregate-functions

解决方案

您可以将 2 个子查询合并为 1 个：

SELECT MAX(c.cust_id) AS max_nh_cust_id,
       MAX(a.avail_balance) AS max_nh_avail_balance 
FROM account a INNER JOIN customer c 
ON a.cust_id = c.cust_id 
WHERE c.state = 'NH'

像这样加入它：

SELECT a.cust_id
FROM account a 
INNER JOIN customer c ON a.cust_id = c.cust_id
INNER JOIN (
  SELECT MAX(c.cust_id) AS max_nh_cust_id,
         MAX(a.avail_balance) AS max_nh_avail_balance 
  FROM account a INNER JOIN customer c 
  ON a.cust_id = c.cust_id 
  WHERE c.state = 'NH'
) t ON c.cust_id > t.max_nh_cust_id AND a.avail_balance > t.max_nh_avail_balance
WHERE c.state = 'MA'

请参阅演示。
结果：

> | cust_id |
> | ------: |
> |      13 |

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