如何从键值对表中选择数据

Question

表A.

id,parentID, key, value
1, 2, name, name1
2, 2, age, 20
3, 2, place, place1

50, 7, name, namex
51, 7, age, 20
52, 7, place, place1
........
101, 5, name, namez
102, 5, age, 23
103, 5, place, place2

我需要以波纹管格式获得plave = place1和age = 20的所有日期

parentid, name, age, place
2, name1, 20, place1
7, namex, 20, place1

如何编写Mysql SQL查询请帮帮我

Answer 1

您可以使用条件聚合将parentid的所有信息都放到一行,然后使用一个where子句来表示所需的条件.

select * from (
select parentid
,max(case when key='name' then value end) as name
,max(case when key='age' then value end) as age
,max(case when key='place' then value end) as place
from tableA
group by parentid 
) t
where place='place1' and age=20

这假设表中每个parentid只有一个键.