Question

我正在查询基于user_id和特定日期和操作的多个表的结果，但我还有一个名为user_notes的单独表：

user_notes

| id |       user_id |                         note |          date |
------------------------------------------------------------------------
|  1 |            10 |                  First note. |    2016-01-01 |
|  2 |            10 |                 Second note. |    2016-01-02 |
|  3 |            11 |                  First note. |    2016-01-03 |
|  4 |            11 |                 Second note. |    2016-01-04 |
|  5 |            11 |                  Third note. |    2016-01-05 |

我想知道当我与其他表连接时，如何将所有这些注释及其日期作为单独的列返回到每个记录/结果中，并且每个user_id只返回一行，因为最终结果看起来如此像这样的东西：

final_result

| user_id |  other_data |       note1 |      date1 |        note2 |      date2 |       note3 |      date3 |...
---------------------------------------------------------------------------------------------------------
|  10     |  .......... | First note. | 2016-01-01 | Second note. | 2016-01-02 |             |            | ...
|  11     |  .......... | First note. | 2016-01-03 | Second note. | 2016-01-04 | Third note. | 2016-01-05 | ...

依此类推......最多可以有10个音符，因此每个音符最多可以有10个额外的音符＆＃34;音符＆＃34;和＆＃34;日期＆＃34;条目。

任何想法如何实现，如果有的话？

Answer 1

这可以通过这个技巧来实现：

select main.user_id, 
  first_note.note as note1, first_note.date,
  second_note.note as note2, second_note.date,
  ...
from user_notes as main
inner join (select * from user_notes where user_id = main.user_id limit 0,1 ) as first_note on main.user_id = first_note.user_id
inner join (select * from user_notes where user_id = main.user_id limit 1,1 ) as second_note on main.user_id = second_note.user_id
...

mySQL如何将多个JOIN结果作为唯一列返回？

1 个答案: