从多个表中的字段创建摘要视图答案

【问题标题】：Creating summary VIEW from fields from multiple tables从多个表中的字段创建摘要视图
【发布时间】：2018-12-11 18:40:45
【问题描述】：

我正在尝试编写用于在 MySQL 中创建视图的选择查询。视图中的每一行都应显示从多个表中收集的用户值的每周摘要（sum、avg）。这些表彼此相似但不相同。该视图还应包括行，以防其他表没有该周的值。像这样的：

| week_year | sum1 | avg1 | sum2 | user_id |
| --------- | ---- | ---- | ---- | ------- |
| 201840    |      |      | 3    | 1       |
| 201844    | 45   | 55   |      | 1       |
| 201845    | 55   | 65   |      | 1       |
| 201849    | 65   | 75   |      | 1       |
| 201849    | 75   | 85   | 3    | 2       |

表格（简化）如下：

CREATE TABLE IF NOT EXISTS `t1` (
  `user_id` INT NOT NULL AUTO_INCREMENT,
  `date` DATE NOT NULL,
  `value1` int(3) NOT NULL,
  `value2` int(3) NOT NULL,
  PRIMARY KEY (`user_id`,`date`)
) DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `t2` (
  `id` INT NOT NULL AUTO_INCREMENT,
  `date` DATE NOT NULL,
  `value3` int(3) NOT NULL,
  PRIMARY KEY (`id`)
) DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `t3` (
  `t3_id` INT NOT NULL,
  `user_id` INT NOT NULL
) DEFAULT CHARSET=utf8;

我目前的解决方案似乎不合理，我不确定在数千行的情况下它会如何执行：

select ifnull(yearweek(q1.date1), yearweek(q1.date2)) as week_year,
       sum(value1)                             as sum1,
       avg(value2)                              as avg1,
       sum(value3)                                   as sum2,
       q1.user_id
from (select t2.date as date2,
             t1.date as date1,
             ifnull(t3.user_id, t1.user_id) as user_id,
             t1.value1,
             t1.value2,
             t2.value3
      from t2
             join t3 on t3.t3_id=t2.id
             left join t1 on yearweek(t1.date) = yearweek(t2.date) and t1.user_id = t3.user_id
      union
      select t2.date as date2,
             t1.date as date1,
             ifnull(t3.user_id, t1.user_id) as user_id,
             t1.value1,
             t1.value2,
             t2.value3
      from t2
             join t3 on t3.t3_id=t2.id
             right join t1 on yearweek(t1.date) = yearweek(t2.date) and t1.user_id = t3.user_id) as q1

group by week_year, user_id;

DB Fiddle

当前的解决方案在性能方面是否还可以，还是有更好的选择？如果将来添加第三个（或第四个）表，我将如何管理查询？我应该考虑创建一个单独的表，用触发器更新吗？

提前致谢。

【问题讨论】：

您可以索引ON或WHERE子句使用的所有表的某些列，这将有助于搜索记录。

标签： mysql join union sqlfiddle create-view

【解决方案1】：

另一种方法是合并所有数据，然后对其进行分组。您必须进行性能测试，看看哪个更好：

SELECT

  yearweek(date), 
  SUM(value1) as sum1,
  AVG(value2) as avg1,
  SUM(value3) as sum2
FROM
(
  SELECT user_id, date, value1, value2, CAST(null as INT) as value3 FROM t1
  UNION ALL 
  SELECT user_id, date, null, null, value3 FROM t2 INNER JOIN t3 ON t2.id = t3.t3_id
)
GROUP BY
  user_id,
  yearweek(date)

希望 mysql 将 null 转换为 int 不会有问题。

【讨论】：