Mysql 如何优化我关于在同一个表中联接3个表的查询？

我想获得从三个月前开始每月购买我产品的id客户。今天是2020-02-15。因此，我希望获得在2019年11月、2019年12月、2020年1月购买的客户

我只有一个表顺序MySQL，如下所示：

SELECT g1.`id_cust`
FROM `orders` g1 
    JOIN `orders` g2
    ON g2.`id_cust`   = g1.`id_cust`
      AND g2.`buy_date` >= STR_TO_DATE(CONCAT('01-', LPAD(MONTH(DATE_SUB(NOW(), INTERVAL 2 MONTH)), 2, '0'), '-', YEAR(DATE_SUB(NOW(), INTERVAL 2 MONTH))), '%d-%m-%Y')
      AND g2.`buy_date` < STR_TO_DATE(CONCAT('01-', LPAD(MONTH(DATE_SUB(NOW(), INTERVAL 1 MONTH)), 2, '0'), '-', YEAR(DATE_SUB(NOW(), INTERVAL 1 MONTH))), '%d-%m-%Y')
    JOIN `orders` g3
    ON g3.`id_cust`   = g1.`id_cust`
      AND g3.`id_cust`   = g2.`id_cust`
      AND g3.`buy_date` >= STR_TO_DATE(CONCAT('01-', LPAD(MONTH(DATE_SUB(NOW(), INTERVAL 1 MONTH)), 2, '0'), '-', YEAR(DATE_SUB(NOW(), INTERVAL 1 MONTH))), '%d-%m-%Y')
      AND g3.`buy_date` < STR_TO_DATE(CONCAT('01-', LPAD(MONTH(NOW()), 2, '0'), '-', YEAR(NOW())), '%d-%m-%Y')
WHERE g1.`buy_date` >= STR_TO_DATE(CONCAT('01-', LPAD(MONTH(DATE_SUB(NOW(), INTERVAL 3 MONTH)), 2, '0'), '-', YEAR(DATE_SUB(NOW(), INTERVAL 3 MONTH))), '%d-%m-%Y')
AND g1.`buy_date` < STR_TO_DATE(CONCAT('01-', LPAD(MONTH(DATE_SUB(NOW(), INTERVAL 2 MONTH)), 2, '0'), '-', YEAR(DATE_SUB(NOW(), INTERVAL 2 MONTH))), '%d-%m-%Y')
GROUP BY g1.`id_cust`

订单表主键=ID自动增量：

-----------------------------------------------
|      ID      |    id_cust  |    buy_date    |
-----------------------------------------------
|       1      |       10    |   2019-11-01   | 
|       2      |       11    |   2019-11-10   |
|       3      |       10    |   2019-12-11   |
|       4      |       12    |   2019-12-12   |
|       5      |       10    |   2020-01-13   |
|       6      |       11    |   2020-01-14   |
|       7      |       12    |   2020-01-15   |
-----------------------------------------------

根据我的要求，答案是id_cust 10

我试过了，结果如下：

SELECT g1.`id_cust`
FROM `orders` g1 
    JOIN `orders` g2
    ON g2.`id_cust`   = g1.`id_cust`
      AND g2.`buy_date` >= STR_TO_DATE(CONCAT('01-', LPAD(MONTH(DATE_SUB(NOW(), INTERVAL 2 MONTH)), 2, '0'), '-', YEAR(DATE_SUB(NOW(), INTERVAL 2 MONTH))), '%d-%m-%Y')
      AND g2.`buy_date` < STR_TO_DATE(CONCAT('01-', LPAD(MONTH(DATE_SUB(NOW(), INTERVAL 1 MONTH)), 2, '0'), '-', YEAR(DATE_SUB(NOW(), INTERVAL 1 MONTH))), '%d-%m-%Y')
    JOIN `orders` g3
    ON g3.`id_cust`   = g1.`id_cust`
      AND g3.`id_cust`   = g2.`id_cust`
      AND g3.`buy_date` >= STR_TO_DATE(CONCAT('01-', LPAD(MONTH(DATE_SUB(NOW(), INTERVAL 1 MONTH)), 2, '0'), '-', YEAR(DATE_SUB(NOW(), INTERVAL 1 MONTH))), '%d-%m-%Y')
      AND g3.`buy_date` < STR_TO_DATE(CONCAT('01-', LPAD(MONTH(NOW()), 2, '0'), '-', YEAR(NOW())), '%d-%m-%Y')
WHERE g1.`buy_date` >= STR_TO_DATE(CONCAT('01-', LPAD(MONTH(DATE_SUB(NOW(), INTERVAL 3 MONTH)), 2, '0'), '-', YEAR(DATE_SUB(NOW(), INTERVAL 3 MONTH))), '%d-%m-%Y')
AND g1.`buy_date` < STR_TO_DATE(CONCAT('01-', LPAD(MONTH(DATE_SUB(NOW(), INTERVAL 2 MONTH)), 2, '0'), '-', YEAR(DATE_SUB(NOW(), INTERVAL 2 MONTH))), '%d-%m-%Y')
GROUP BY g1.`id_cust`

请帮助我简化我的语法，因为当它在大量数据上运行时，速度非常慢，或者如果我的语法错误，请更正我的语法。

这怎么样

select c.id_cust
from (select o.id_cust, year(buy_date) as yyyy, month(buy_date) as mm,
             row_number() over (partition by o.id_cust) as month_counter
      from orders o
      where buy_date >= date_format(current_date - interval 3 month, '%Y-%m-%d') and
            buy_date < date_format(current_date, '%Y-%m-%d')
      group by id_cust, yyyy, mm
     ) c
where month_counter = 3;

这只会过滤到你关心的三个月。然后它按年份和月份进行聚合，只返回第三行

事实上，这更容易表达为：

select o.id_cust
from orders o
where buy_date >= date_format(current_date - interval 3 month, '%Y-%m-%d') and
      buy_date < date_format(current_date, '%Y-%m-%d')
group by o.id_cust
having count(distinct year(buy_date), month(buy_date)) = 3;

---

我将使用戈登的第二个问题。但是，如果您的代码作为练习使用，您可以通过在buy_date、id_cust和id_cust、buy_date上创建索引来优化执行时间。第一个用于WHERE子句，第二个用于ON子句

使用此模式

CREATE TABLE orders (
  `ID` INTEGER primary key,
  `id_cust` INTEGER,
  `buy_date` VARCHAR(10)
);

查询的解释结果是

| id  | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra                                              |
| --- | ----------- | ----- | ---------- | ---- | ------------- | --- | ------- | --- | ---- | -------- | -------------------------------------------------- |
| 1   | SIMPLE      | g1    |            | ALL  |               |     |         |     | 7    | 14.29    | Using where; Using temporary; Using filesort       |
| 1   | SIMPLE      | g2    |            | ALL  |               |     |         |     | 7    | 14.29    | Using where; Using join buffer (Block Nested Loop) |
| 1   | SIMPLE      | g3    |            | ALL  |               |     |         |     | 7    | 14.29    | Using where; Using join buffer (Block Nested Loop) |

没有使用任何键，块嵌套循环听起来非常糟糕

在添加索引之后

ALTER TABLE orders ADD INDEX (buy_date, id_cust);
ALTER TABLE orders ADD INDEX (id_cust, buy_date);

它现在看起来好多了，尽管它决定不使用我的第一个索引，可能是因为GROUPBY

然后，我会将查询简化为：

SELECT DISTINCT g1.id_cust
FROM orders g1 
    JOIN orders g2 ON g2.id_cust = g1.id_cust
    JOIN orders g3 ON g3.id_cust = g1.id_cust
    -- AND g3.id_cust  = g2.id_cust -- redundant condition
WHERE g1.buy_date >= DATE_FORMAT(NOW() - INTERVAL 3 MONTH, '%Y-%m-01')
  AND g1.buy_date <  DATE_FORMAT(NOW() - INTERVAL 2 MONTH, '%Y-%m-01')
  AND g2.buy_date >= DATE_FORMAT(NOW() - INTERVAL 2 MONTH, '%Y-%m-01')
  AND g2.buy_date <  DATE_FORMAT(NOW() - INTERVAL 1 MONTH, '%Y-%m-01')
  AND g3.buy_date >= DATE_FORMAT(NOW() - INTERVAL 1 MONTH, '%Y-%m-01')
  AND g3.buy_date <  DATE_FORMAT(NOW() - INTERVAL 0 MONTH, '%Y-%m-01')
-- GROUP BY g1.id_cust -- You can use DISTINCT instead

---

您在HAVING子句中缺少“=3”，在第一个查询中将select o.id\u cust更改为select c.id\u cust-是的，我在HAVING子句中缺少“=3”，请您回答，但为了得到我想要的。。您必须将日期格式更改为“%Y-%m-01”@RikcatKristianLumbanGaol。我注意到你没有接受这个答案。这不是编写代码最有效的方法吗？