Question

我有如下所示的表格结构。该数据库是MariaDB。

+-----------+----------+--------------+-----------------+
| id_object |   name   | value_double | value_timestamp |
+-----------+----------+--------------+-----------------+
|     1     | price    | 1589         |  null           |
|     1     | payment  | 1590         |  null           |
|     1     | date     | null         |  2012-04-17     |
|     2     | price    | 1589         |  null           |
|     2     | payment  | 1590         |  null           |
|     2     | date     | null         |  2012-04-17     |
|     3     | price    | 1589         |  null           |
|     3     | payment  | 1590         |  null           |
|     3     | date     | null         |  2012-09-25     |
|    ...    | ...      | ...          |  ..             |
+-----------+----------+--------------+-----------------+

1）我需要通过三个条目获得重复项：price＆amp;付款＆amp;日期;
例如：id_object = 2的记录是重复的，因为价格，付款和日期与id_object = 1的记录的值相同。 id_object = 3的记录不重复，因为日期不同（2012-09-25！= 2012-04-17）
2）除了一份副本外，我应删除重复项。

我想做三个选择操作并加入id_object上的每个选择。我可以通过一个条目（价格|付款|日期）获得重复项。我遇到了做连接的问题

SELECT `id_object`,`name`,{P.`value_double` | P.`value_timestamp`}
FROM record P
INNER JOIN(
SELECT {value_double | value_timestamp}
FROM record
WHERE name = {required_entry}
GROUP BY {value_double | value_timestamp}
HAVING COUNT(id_object) > 1
)temp ON {P.value_double = temp.value_double | P.value_timestamp = temp.value_timestamp}
WHERE name = {required_entry}

有人可以帮助并展示纯粹（更好）的解决方案吗？

Answer 1

我只会将group_concat()值组合在一起并按此方式进行测试：

 select t.*
 from t join
      (select min(id_object) id_object
       from (select id_object,
                    group_concat(name, ':', coalesce(value_double, ''), ':', coalesce(value_timestamp, '') order by name) pairs
             from t
             where name in ('price', 'payment', 'date')
             group by id_object
            ) tt
        group by pairs
     ) tt
     on t.id_object = tt.id_object;

要为每组相关值实际删除不是最小id的那些：

delete t
    from t left join
         (select min(id) as id
          from (select id, group_concat(name, ':', coalesce(value_double, ''), ':', coalesce(value_timestamp, '' order by name) as pairs,
                from t
                where name in ('price', 'payment', 'date')
                group by id
               ) tt
          group by pairs
         ) tt
         on t.id = tt.id
    where tt.id is null;

Answer 2

虽然效率低于某些替代方案，但我发现沿着这些方法的方法更容易阅读...

SELECT MIN(id_object) id_object
     , price
     , payment
     , date 
  FROM 
     ( SELECT id_object
            , MAX(CASE WHEN name = 'price'   THEN value_double END) price
            , MAX(CASE WHEN name = 'payment' THEN value_double END) payment
            , MAX(CASE WHEN name = 'date'    THEN value_timestamp END) date
         FROM eav
        GROUP 
           BY id_object
     ) x
 GROUP  
    BY price
     , payment
     , date;

从表mysql

2 个答案: