使用SQL从行中的值创建列
使用SQL从行中的值创建列
提问于 2019-05-22 07:11:10
有人能帮我用sql连接两个表吗？在连接之后，行应该显示为列，如下所示。
我有两张表T1和T2
T1
------------
Id. Name date
--------------
1 AAA 2019-05-06
2 BBB 2019-05-06
T2
---------------
Id. attr_name. attr_value. date
--------------------
1 . PP0 8 2019-05-06
1 . PD0 125.00 2019-05-06
1 PP1 2 2019-05-06
1 PD1 150.00 2019-05-06
3 PP0 5 2019-05-06
3 PD1 50.00 2019-05-06如果有PP0，就会有对应的PD0
My output should be
---------------------
Id Name attr_pp_name attr_pp_value. attr_pd_name attr_pd_value
1 AAA PP0 8 PD0 125.00
1. AAA PP1 2 PD1 150.00我尝试了下面的查询
select t.Id, t.name ea.attr_name ,ea.attr_value, ea1.attr_name, ea1.attr_value from T1 t
INNER JOIN T2 ea ON t.id = ea.id AND ea.attr_name IN ('PP0', 'PP1')
INNER JOIN T2 ea1 ON t.id = ea.id AND ea.attr_name IN ('PD0', 'PD1');但是上面的查询给出了重复的结果，如
Id Name attr_pp_name attr_pp_value. attr_pd_name attr_pd_value
1 AAA PP0 8 PD0 125.00
1. AAA PP1 2 PD1 150.00
1 AAA PP0 2 PD1 150.00
1. AAA PP1 8 PD0 125.00回答 1
Stack Overflow用户
发布于 2019-05-22 07:24:28
在MySQL 8+中，您可以使用窗口函数枚举属性值，然后聚合：
select t.*,
max(case when ea.attr_name like 'PP%' then ea.attr_name end),
max(case when ea.attr_name like 'PP%' then ea.attr_value end),
max(case when ea.attr_name like 'PD%' then ea.attr_name end),
max(case when ea.attr_name like 'PD%' then ea.attr_value end)
from T1 t join
(select ea.*,
row_number() over (partition by ea.id, left(ea.attr_name, 2) order by ea.id) as seqnum
from t2 ea
) ea
on ea.id = t.id
group by t.id, ea.seqnum;编辑：
在早期版本中，解决此问题的一种方法是使用变量：
select t.*,
max(case when ea.attr_name like 'PP%' then ea.attr_name end),
max(case when ea.attr_name like 'PP%' then ea.attr_value end),
max(case when ea.attr_name like 'PD%' then ea.attr_name end),
max(case when ea.attr_name like 'PD%' then ea.attr_value end)
from T1 t join
(select ea.*,
(@rn := if(@ida = concat_ws(':', ea.id, left(ea.attr_name, 2)), @rn + 1,
if(@ida := concat_ws(':', ea.id, left(ea.attr_name, 2)), 1, 1)
)
) as seqnum
from (select ea.*
from t2 ea
order by ea.id, left(ea.attr_name, 2)
) ea cross join
(select @ida := '', @rn := 0) params
) ea
on ea.id = t.id
group by t.id, ea.seqnum;页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/56247387
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