Mysql 排序依据与分组

Question

大家好，今天我遇到了一个问题..

首先我有两个表，每个表都有“product_seq_id”列，并且我使用相同的“product_seq_id”加入表 在第二个表中，“product_seq_id”有多行，我只想要一个具有以下条件的行

• table2.date_start 不为空
• table2.date_start 等于“0000-00-00”或 table2.date_start <= CURDATE()
• table2.date_end 等于“0000-00-00”或 table2.date_start >= CURDATE()
• 如果同一天有 2 行或更多行匹配，则获得最高的 table2.priority

我已经做了一些工作..但问题在于，在对分组进行排序时，它没有采用最高优先级编号

//我的查询

SELECT 
    psp . *, pcp . *
FROM
    sk_product_category_path pcp
        left join
    sk_product_special_price psp ON (psp.product_seq_id = pcp.product_seq_id)
where
    pcp.category_seq_id = 146
        AND psp.product_seq_id IS NOT NULL
        AND CASE
        WHEN
            psp.date_start IS NOT NULL
        THEN
            (psp.date_start = '0000-00-00'
                OR psp.date_start <= CURDATE())
                AND (psp.date_end = '0000-00-00'
                OR psp.date_end >= CURDATE())
        ELSE 1 = 1
    END
group by psp.product_seq_id
order by psp.priority desc

<小时/>

Result Came for above code:
# product_special_price_seq_id, product_special_price, date_start, date_end, priority, product_seq_id, product_category_path_seq_id, product_seq_id, category_seq_id
2309    123123  0000-00-00  0000-00-00  0   3196    1   3196    146
2307    12313   0000-00-00  0000-00-00  0   3197    3   3197    146

<小时/>

Result I wanted:
# product_special_price_seq_id, product_special_price, date_start, date_end, priority, product_seq_id, product_category_path_seq_id, product_seq_id, category_seq_id
2309    12200   0000-00-00  0000-00-00  1   3196    2   3196    146
2307    12313   0000-00-00  0000-00-00  0   3197    3   3197    146

//表格数据

CREATE TABLE IF NOT EXISTS `sk_product_category_path` (
  `product_category_path_seq_id` int(11) NOT NULL AUTO_INCREMENT,
  `product_seq_id` int(11) NOT NULL,
  `category_seq_id` int(11) NOT NULL,
  PRIMARY KEY (`product_category_path_seq_id`),
  UNIQUE KEY `product_seq_id` (`product_seq_id`,`category_seq_id`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=4 ;

INSERT INTO `sk_product_category_path` (`product_category_path_seq_id`, `product_seq_id`, `category_seq_id`) VALUES
(1, 3196, 146),
(2, 3197, 146),
(3, 3198, 146);

CREATE TABLE IF NOT EXISTS `sk_product_special_price` (
  `product_special_price_seq_id` int(11) NOT NULL AUTO_INCREMENT,
  `product_special_price` bigint(20) DEFAULT NULL,
  `date_start` date DEFAULT NULL,
  `date_end` date DEFAULT NULL,
  `priority` int(11) DEFAULT NULL,
  `product_seq_id` int(11) NOT NULL,
  PRIMARY KEY (`product_special_price_seq_id`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=4 ;

INSERT INTO `sk_product_special_price` (`product_special_price_seq_id`, `product_special_price`, `date_start`, `date_end`, `priority`, `product_seq_id`) VALUES
(1, 12313, '0000-00-00', '0000-00-00', 0, 3197),
(2, 12200, '2014-02-11', '2014-02-11', 1, 3197),
(3, 123123, '0000-00-00', '0000-00-00', 0, 3196);

Answer 1

在 MySQL 中的 GROUP BY 期间，除非您使用聚合函数，否则它会为每个组选择第一个匹配的行。第一个匹配不必总是带有 min(id) 的行。

可能的查询应该类似于:

SELECT t.*
from table_name t 
inner join (
  select min(id) as id 
  from table_name t 
  group by col) as s
on s.id = t.id