Question

表1

|id | name |

|1 | Test |

|2 | Hello|

|3 | Hii |

表2

|id | related_id | date | time

|1 | 1 | 2014-09-11 | 12.56.25

|2 | 2 | 2014-09-11 | 12.56.25

|3 | 2 | 2014-09-12 | 11.56.25

|4 | 2 | 2014-09-12 | 12.56.31 (Last record)

输出

|id | name | date | time

|1 | test | 2014-09-11 | 12.56.25

|2 | Hello | 2014-09-12 | 12.56.31 (This is the last record from table 2)

|3 | Hii | - | -

输出表中的SO，Id = 2是表2的最后一条记录，其中相对id = 2 ...我也想要表1中的所有记录。

那么我可以使用哪种加入查询？

Answer 1

您可以使用table2的自联接来获取每个related_id组的最后一行，并使用带内部选择的左连接和table1

select a.*,
d.`date`,
d.`time`
from table1 a
left join (
    select b.* 
    from table2 b
    inner join (
                select 
                max(id) id ,
                related_id 
                from table2 
                group by related_id ) c
      on(b.id=c.id and b.related_id = c.related_id)
  ) d
on(a.id = d.related_id)

Demo

另一种方法是使用substring_index和group_concat按顺序使用

select a.*,
substring_index(group_concat(b.`date` order by b.id desc),',',1) `date`,
substring_index(group_concat(b.`time` order by b.id desc),',',1) `time`
from table1 a
left join table2 b
on(a.id = b.related_id)
group by a.id

Demo 2

如何在mysql中使用JOIN Query获取Distinct Value以及最后一条记录？

1 个答案: