MySQL

Question

即使经过数小时的搜索和尝试，我仍然无法弄清楚这一点。可能是我选词不对？

好的，所以我 table 遇到了这样的事件：

EVENT
+----+------------+------------+------+
| id | id_article | id_section | date |
+----+------------+------------+------+
|  1 |          1 |          1 | 2011 |
|  2 |          1 |          3 | 2012 |
|  3 |          2 |          7 | 2013 |
|  4 |          2 |          6 | 2014 |
|  5 |          3 |         14 | 2015 |
|  6 |          3 |         13 | 2016 |
|  7 |          3 |          0 | 2017 |
+----+------------+------------+------+

我想将此 table 分为三个不同的列，其中每列包含最新事件（id_section 和日期) 在 id_section 的列表中。嗯，基本上是这样的：

sectionA = id_section IN (1,2,3,4,5) and MAX(date)

sectionB = id_section IN (6,7,8,9,10) and MAX(date)

sectionC = id_section IN (11,12,13,14,15) and MAX(date)

DESIRED RESULT
+------------+----------+----------+-----------+
| id_article | sectionA | sectionB | sectionC  | #id_event
+------------+----------+----------+-----------+
|          1 | 3 (2012) | null     | null      | #id 2
|          2 | null     | 6 (2014) | null      | #id 4
|          3 | 0 (2017) | null     | 13 (2016) | #id 7, 6 <-- two latest events
+------------+----------+----------+-----------+

这是我现在拥有的 SqlFiddle - 它只选择每个 id_article:

的最新事件

INSUFFICIENT RESULT
+------------+----------+----------+-----------+
| id_article | sectionA | sectionB | sectionC  | #id_event
+------------+----------+----------+-----------+
|          1 | 3 (2012) | null     | null      | #id 2
|          2 | null     | 6 (2014) | null      | #id 4
|          3 | 0 (2017) | null     | null      | #id 7 <-- only latest event
+------------+----------+----------+-----------+

我尝试使用更多的 JOINS，但我还是想不通。

感谢您的帮助！

Answer 1

根据您当前的查询，如果每个 id_article 上有多个部分，我对子查询做了一些更改以确定最大值。此外，0 应包含在 SectionA

的列表中

SELECT e1.id_article, 
       MAX(CASE WHEN section = 'SectionA' 
                THEN CONCAT(e2.id_section, ' (', e2.date, ')') END) AS sectionA, 
       MAX(CASE WHEN section = 'SectionB' 
                THEN CONCAT(e2.id_section, ' (', e2.date, ')') END) AS sectionB, 
       MAX(CASE WHEN section = 'SectionC'
                THEN CONCAT(e2.id_section, ' (', e2.date, ')') END) AS sectionC
  FROM event e1
 INNER JOIN (SELECT a.id_article,
                    a.id_section,       
                    a.`date`,
                    a.section,
                    COUNT(*) row_number
               FROM (SELECT *,
                            CASE WHEN id_section IN (0,1,2,3,4,5)
                                 THEN 'SectionA'
                                 WHEN id_section IN (6,7,8,9,10)
                                 THEN 'SectionB'
                                 WHEN id_section IN (11,12,13,14,15)
                                 THEN 'SectionC'
                             END section
                       FROM `event`) a
              INNER JOIN  (SELECT *,
                                  CASE WHEN id_section IN (0,1,2,3,4,5)
                                       THEN 'SectionA'
                                       WHEN id_section IN (6,7,8,9,10)
                                       THEN 'SectionB'
                                       WHEN id_section IN (11,12,13,14,15)
                                       THEN 'SectionC'
                                   END section
                             FROM `event`) b
                 ON a.id_article = b.id_article
                AND a.section = b.section
                AND a.`date` <= b.`date`
              GROUP BY a.id_article,
                       a.id_section,       
                       a.`date`
            ) e2
    ON e1.id_article = e2.id_article 
   AND e1.date = e2.date
 WHERE e2.row_number = 1
 GROUP BY e1.id_article

结果

id_article  sectionA    sectionB    sectionC
1           3 (2012)    (null)      (null)
2           (null)      6 (2014)    (null)
3           0 (2017)    (null)      13 (2016)

MySQL - 根据每列的最新日期和 ID 列表将行转换为列

MySQL - Convert rows into columns based on latest date and list of ids for each column

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