MYSQL子查询与Join-两者对我都不好

我正在使用MYSQL。 我有三张桌子

人员

表，由两列组成：

• id-表中的主键
• 姓名-人员姓名

收入

表，其中包含人员表中人员的收入。 此表中的每条记录代表一个人的收入。 在此表中，一个人可能没有或有很多收入。 表格结构为：

• 人员id（“人员”表的外键）
• 金额（十进制类型-金额）
• 金额的小时数（整数类型-赚取此收入所需的小时数）

费用

包含人员费用的表格。 此表中的每条记录表示一个人的支出， 他花了一笔钱买了多少东西。 一个人在此表中可以有零个或多个费用记录。 表格结构为：

• 人员id（“人员”表的外键）
• 金额（十进制类型的金额）
• 购买的物品数量（整数类型-此费用中购买的物品数量）

我想做的是创建一个查询，它会给我一个所有人的列表 （每人一份记录）每行我都有

• 此人的姓名
• 他所有收入的总和
• 他工作的总小时数
• 他所有费用的总和
• 他买的东西的总数

我尝试的第一种天真的方法逻辑性很好，但性能很差， 它看起来像这样：

SELECT name, income_sum, work_hours_sum, expenses_sum, items_count
FROM (people
      LEFT JOIN 
           (SELECT person_id, sum(amount) as income_sum, 
                   sum(number_of_hours_for_amount) as work_hours_sum
            FROM income
            GROUP BY person_id) as income_subquery
      ON people.id = income_subquery.person_id)

LEFT JOIN
     (SELECT person_id, sum(amount) as expenses_sum, 
             sum(number_of_items_bought) as items_count
      FROM expenses
      GROUP BY person_id) as income_subquery
ON people.id = income_subquery.person_id

据我所知，这个查询的问题是，一旦我从子查询中获得数据，连接的效率就会非常低 因为这些表是临时子查询表，所以在这些表上没有很好地使用索引

充分利用现有索引的最佳方法是直接在三个表之间进行连接 而不是通过子查询。 但这不是一个正确的解决方案，因为它将创建一个笛卡尔积，该积将向聚合和添加重复的值 从那些比他们应该看到的更多的记录中

（我尝试的另一个选择是将每个人的收入和支出值计算为一个select_表达式。） 在SELECT部分（依赖子查询）。这也没有足够快地工作）

---

我正在寻找一个高效的查询并给出这些结果。

试试这个。两个联接都应该使用

people.id

上的索引

SELECT name, income_sum, work_hours_sum, expenses_sum, items_count
FROM people

LEFT JOIN 
     (SELECT person_id, sum(amount) as income_sum, 
             sum(number_of_hours_for_amount) as work_hours_sum
      FROM income
      GROUP BY person_id) as income_subquery
ON people.id = income_subquery.person_id

LEFT JOIN
     (SELECT person_id, sum(amount) as expenses_sum, 
             sum(number_of_items_bought) as items_count
      FROM expenses
      GROUP BY person_id) as expenses_subquery
ON people.id = expenses_subquery.person_id

理想情况下，一个好的查询优化器会意识到您的原始SQL与此等价。但是您使用的是MySQL，所以我不希望进行理想的优化

---

请确保您在

收入、人员id

和

费用、人员id

上有索引，这样子查询中的分组将非常有效。

类似的内容将使您非常接近：

select id, name, (select sum(amount) from income i where i.person_id = p.id) as 'total_income_amount',
                 (select sum(number_of_hours_for_amount) from income i where i.person_id = p.id) as 'total_number_of_hours_for_amount',
                 (select sum(amount) from expenses e where e.person_id = p.id) as 'total_expenses_amount',
                 (select sum(number_of_items_bought) from expenses e where e.person_id = p.id) as 'total_number_of_items_bought'
from   people p;

---

你是对的，这里有一个不可避免的笛卡尔积。您可以将此问题分解为两个子查询：

一项收入：

SELECT p.id, p.name, SUM(i.amount) AS income_sum, SUM(number_of_hours_for_amount) AS work_hours_sum
FROM people p
LEFT JOIN income i ON p.id = i.person_id
GROUP BY p.id;

+----+---------+------------+----------------+
| id | name    | income_sum | work_hours_sum |
+----+---------+------------+----------------+
|  1 | Groucho |      20.00 |             20 |
|  2 | Harpo   |      40.00 |             40 |
|  3 | Chico   |      60.00 |             60 |
+----+---------+------------+----------------+

下面是对该查询的解释：

+----+-------------+-------+------+---------------+------+---------+------+------+----------------------------------------------------+
| id | select_type | table | type | possible_keys | key  | key_len | ref  | rows | Extra                                              |
+----+-------------+-------+------+---------------+------+---------+------+------+----------------------------------------------------+
|  1 | SIMPLE      | p     | ALL  | PRIMARY       | NULL | NULL    | NULL |    3 | Using temporary; Using filesort                    |
|  1 | SIMPLE      | i     | ALL  | NULL          | NULL | NULL    | NULL |    6 | Using where; Using join buffer (Block Nested Loop) |
+----+-------------+-------+------+---------------+------+---------+------+------+----------------------------------------------------+

一项费用：

SELECT p.id, SUM(e.amount) AS expenses_sum, SUM(number_of_items_bought) AS items_count
FROM people p
LEFT JOIN expenses e ON p.id = e.person_id
GROUP BY p.id;

+----+--------------+-------------+
| id | expenses_sum | items_count |
+----+--------------+-------------+
|  1 |        30.00 |           4 |
|  2 |        30.00 |           4 |
|  3 |        30.00 |           4 |
+----+--------------+-------------+

下面是解释：

+----+-------------+-------+------+---------------+------+---------+------+------+----------------------------------------------------+
| id | select_type | table | type | possible_keys | key  | key_len | ref  | rows | Extra                                              |
+----+-------------+-------+------+---------------+------+---------+------+------+----------------------------------------------------+
|  1 | SIMPLE      | p     | ALL  | PRIMARY       | NULL | NULL    | NULL |    3 | Using temporary; Using filesort                    |
|  1 | SIMPLE      | e     | ALL  | NULL          | NULL | NULL    | NULL |    6 | Using where; Using join buffer (Block Nested Loop) |
+----+-------------+-------+------+---------------+------+---------+------+------+----------------------------------------------------+

我们在上面的解释报告中看到，查询在收入和支出表上使用表扫描（键入“ALL”），并在没有索引的情况下进行联接（“使用联接缓冲区”）。红色标志是连接中涉及两个表，其中两个表都使用了访问类型“ALL”。如果这些表中的行数不多，那么成本就会非常高。它通常伴随着“使用联接缓冲区”，这是一个代价高昂的查询的另一个危险信号

最后，它通过使用临时表和文件排序来低效地执行组。这是另一个性能杀手

是一个MySQL 5.6的东西。如果使用早期版本的MySQL，您将看不到这一点

以下索引应有助于使这些查询变得更好：

ALTER TABLE income ADD KEY (person_id, amount, number_of_hours_for_amount);
ALTER TABLE expenses ADD KEY (person_id, amount, number_of_items_bought);

现在解释报告不再显示低效的访问。连接使用索引（类型“ref”）完成，临时表和文件排序消失。“使用索引”表示它仅通过索引中的列访问连接的表，根本不需要触摸表行

+----+-------------+-------+-------+---------------+-----------+---------+-----------+------+-------------+
| id | select_type | table | type  | possible_keys | key       | key_len | ref       | rows | Extra       |
+----+-------------+-------+-------+---------------+-----------+---------+-----------+------+-------------+
|  1 | SIMPLE      | p     | index | PRIMARY       | PRIMARY   | 4       | NULL      |    3 | NULL        |
|  1 | SIMPLE      | i     | ref   | person_id     | person_id | 5       | test.p.id |    1 | Using index |
+----+-------------+-------+-------+---------------+-----------+---------+-----------+------+-------------+

+----+-------------+-------+-------+---------------+-----------+---------+-----------+------+-------------+
| id | select_type | table | type  | possible_keys | key       | key_len | ref       | rows | Extra       |
+----+-------------+-------+-------+---------------+-----------+---------+-----------+------+-------------+
|  1 | SIMPLE      | p     | index | PRIMARY       | PRIMARY   | 4       | NULL      |    3 | NULL        |
|  1 | SIMPLE      | e     | ref   | person_id     | person_id | 5       | test.p.id |    1 | Using index |
+----+-------------+-------+-------+---------------+-----------+---------+-----------+------+-------------+

您说过要在一个查询中完成此操作，下面是如何完成此操作：

我们可以将这两个单独的查询合并到一个查询中，以获得每人一行的结果：

SELECT name, income_sum, work_hours_sum, expenses_sum, items_count
FROM
(SELECT p.id, p.name, SUM(i.amount) AS income_sum, SUM(number_of_hours_for_amount) AS work_hours_sum
 FROM people p
 LEFT OUTER JOIN income i ON p.id = i.person_id
 GROUP BY p.id) AS subq_i
INNER JOIN
(SELECT p.id, SUM(e.amount) AS expenses_sum, SUM(number_of_items_bought) AS items_count
 FROM people p
 LEFT OUTER JOIN expenses e ON p.id = e.person_id
 GROUP BY p.id) AS subq_e
USING (id);

+---------+------------+----------------+--------------+-------------+
| name    | income_sum | work_hours_sum | expenses_sum | items_count |
+---------+------------+----------------+--------------+-------------+
| Groucho |      20.00 |             20 |        30.00 |           4 |
| Harpo   |      40.00 |             40 |        30.00 |           4 |
| Chico   |      60.00 |             60 |        30.00 |           4 |
+---------+------------+----------------+--------------+-------------+

即使对于这个联合查询，解释看起来也没那么糟糕。没有临时表、文件队列或联接缓冲区，并且很好地使用了覆盖索引

+----+-------------+------------+-------+---------------+-------------+---------+-----------+------+-------------+
| id | select_type | table      | type  | possible_keys | key         | key_len | ref       | rows | Extra       |
+----+-------------+------------+-------+---------------+-------------+---------+-----------+------+-------------+
|  1 | PRIMARY     | <derived2> | ALL   | NULL          | NULL        | NULL    | NULL      |    3 | NULL        |
|  1 | PRIMARY     | <derived3> | ref   | <auto_key0>   | <auto_key0> | 4       | subq_i.id |    2 | NULL        |
|  3 | DERIVED     | p          | index | PRIMARY       | PRIMARY     | 4       | NULL      |    3 | Using index |
|  3 | DERIVED     | e          | ref   | person_id     | person_id   | 5       | test.p.id |    1 | Using index |
|  2 | DERIVED     | p          | index | PRIMARY       | PRIMARY     | 4       | NULL      |    3 | NULL        |
|  2 | DERIVED     | i          | ref   | person_id     | person_id   | 5       | test.p.id |    1 | Using index |
+----+-------------+------------+-------+---------------+-------------+---------+-----------+------+-------------+

+----+-------------+------------+-------+---------------+-------------+---------+-----------+------+-------------+
|id |选择|类型|类型|可能的|键|键|列|参考|行|额外|
+----+-------------+------------+-------+---------------+-------------+---------+-----------+------+-------------+
|1 | PRIMARY | ALL | NULL | NULL | NULL | NULL | 3 | NULL|
|1 |主| | | | | | |参考| | | 4 |子Q|U i.id | 2 |空|
|3 |派生| p |索引|主|主| 4 |空| 3 |使用索引|
|3 |导出| e |参考|人员| id |人员| id | 5 |测试p.id | 1 |使用索引|
|2 |派生| p |索引|主|主| 4 |空| 3 |空|
|2 |衍生| i |参考|个人| id |个人| id | 5 |测试p.id | 1 |使用索引|
+----+-------------+------------+-------+---------------+-------------+---------+-----------+------+-------------+

也许您可以完全跳过连接

SELECT person_id
     , MIN(name) AS name
     , SUM(income_sum) AS income_sum
     , SUM(work_hours_sum) AS work_hours_sum
     , SUM(expenses_sum) AS expenses_sum
     , SUM(items_count) AS items_count
FROM (
SELECT id AS person_id
     , name
     , NULL AS income_sum
     , NULL AS work_hours_sum
     , NULL AS expenses_sum
     , NULL AS items_count
  FROM people
UNION ALL
SELECT person_id
     , NULL AS name
     , sum(amount) AS income_sum
     , sum(number_of_hours_for_amount) AS work_hours_sum
     , NULL AS expenses_sum
     , NULL AS items_count
  FROM income
 GROUP BY person_id
UNION ALL
SELECT person_id
     , NULL AS name
     , NULL AS income_sum
     , NULL AS work_hours_sum
     , sum(amount) AS expenses_sum
     , sum(number_of_items_bought) AS items_count
  FROM expenses
 GROUP BY person_id
) as d
WHERE person_id IS NOT NULL -- my sql generates this row
 GROUP BY person_id

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您多久更新一次收入和支出？你能把它们的总和聚合到另一个表中吗？表中有多少行？“不快”有多慢？你能把解释贴出来吗