[英]MYSQL select query for most frequent product?
我需要幫助找出如何只為每個分支顯示最常用的產品。
這適用於DB中的每個分支。
PS:這是在一個表中完成的(此性能不需要其他表),並且只需要提到的兩個屬性。
基於Sean的DB示例,我已經創建了查詢,它可以完成這項工作,但是,請注意您在應用程序中的運行方式看起來資源昂貴。 嘗試考慮另一種方法來發現最常見的產品,而不是數據庫查詢。
SELECT
a.branch_id, `branch_product` , COUNT(branch_product) AS cnt , b.mx
FROM
branch_products a
LEFT JOIN
(SELECT
branch_id, MAX(cnt) AS mx
FROM
(SELECT branch_id, COUNT(branch_product) AS cnt FROM branch_products GROUP BY branch_id, branch_product ) AS maxes
GROUP BY branch_id) b
ON a.branch_id = b.branch_id
GROUP BY branch_id, branch_product
HAVING cnt=mx
將計數放在子查詢中,ORDER BY計數DESC,然后在子查詢GROUP BY之外的分支ID:
SELECT * FROM (
SELECT *, count(branch_product) AS cou FROM branch_products
GROUP BY branch_id, branch_product
ORDER BY cou DESC
) AS ordbycou
GROUP BY branch_id
產量:
+-----------+----------------+-----+
| branch_id | branch_product | cou |
+-----------+----------------+-----+
| 1 | trainers | 3 |
| 2 | suit | 2 |
| 3 | suit | 1 |
+-----------+----------------+-----+
3 rows in set (0.00 sec)
這是一個用於嘗試以上查詢的示例表:
SET SQL_MODE="NO_AUTO_VALUE_ON_ZERO";
CREATE TABLE IF NOT EXISTS `branch_products` (
`branch_id` mediumint(8) unsigned NOT NULL,
`branch_product` varchar(128) NOT NULL,
KEY `branch_id` (`branch_id`),
KEY `branch_product` (`branch_product`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
INSERT INTO `branch_products` (`branch_id`, `branch_product`) VALUES
(1, 'trainers'),
(1, 'trainers'),
(1, 'trainers'),
(1, 'tie'),
(1, 'tie'),
(1, 'suit'),
(2, 'suit'),
(2, 'suit'),
(2, 'tie'),
(3, 'suit');
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