Question

自学习的初学者MySql ..我需要带回parent_ids匹配的所有行，但是年份没有。问题是，GROUP BY只为每个parent_id返回一行，我想要所有（所以，我一直在使用2个查询，并将结果从第一个粘贴到第二个）我如何在一个查询中执行此操作？

我有：

id  parent_id   year
aa1 aa          2010
aa3 aa          2011
bb1 bb          2010
bb2 bb          2011
cc1 cc          2010
cc2 cc          2010

我需要回复：

id  parent_id   year
aa1 aa          2010
aa3 aa          2011
bb1 bb          2010
bb2 bb          2011

当前第一个查询：

SELECT id, name, `year`, parent_id
FROM t1
GROUP BY parent_id
HAVING COUNT(DISTINCT `year`) > 1

然后我使用IN：

将结果粘贴到一个简单的选择查询中

SELECT id, parent_id, name, `year`
FROM t1
WHERE parent_id IN ('......',')

Answer 1

一个选项可能是使用子查询。例如：

SELECT id, name, year, parent_id
FROM t1
WHERE parent_id IN (SELECT parent_id
FROM t1
GROUP BY parent_id
HAVING COUNT(DISTINCT year) > 1)

如果要多次查询，您也可以使用视图。 http://www.w3schools.com/sql/sql_view.asp

Answer 2

未启用ONLY_FULL_GROUP_BY模式时

SELECT id, parent_id, `year`
FROM test
GROUP BY parent_id, `year`
HAVING COUNT(*) = 1;

启用ONLY_FULL_GROUP_BY模式时

SELECT ANY_VALUE(id), parent_id, `year`
FROM test
GROUP BY parent_id, `year`
HAVING COUNT(*) = 1;

返回的结果是

+---------------+-----------+------+
| ANY_VALUE(id) | parent_id | year |
+---------------+-----------+------+
| aa1           | aa        | 2010 |
| aa3           | aa        | 2011 |
| bb1           | bb        | 2010 |
| bb2           | bb        | 2011 |
+---------------+-----------+------+

Answer 3

SELECT  id, parent_id, year
    FROM  t1
    JOIN  
      ( SELECT  parent_id
            FROM  t1
            GROUP BY  parent_id
            HAVING  COUNT(DISTINCT year) > 1 ) AS b USING(parent_id
      );

（假设IN ( SELECT ... )被编入索引，JOIN比parent_id效率更高。）

或者您可能会发现GROUP_CONCAT更有趣：

SELECT  parent_id, GROUP_CONCAT(DISTINCT year) AS years
    FROM  t1;
    GROUP BY  parent_id
    HAVING  LENGTH(years) > 4;

Answer 4

尝试此查询：

select a.id , a.parent_id , a.year
from t1 a join t1 b
on a.id <> b.id and a.parent_id=b.parent_id and a.year<>b.year;

MySQL - GROUP By和DISTINCT，但返回所有行？

4 个答案: