MySQL一对多关系单查询

Question

I have this two tables. I'll make it as simple as possible:

Sample value in main_table:
id = 1

Sample value in details_table:
id = 1
type = book
name = harry potter

id = 1
type = paper
name = post it

The result I need is to get id with the name for those two types.

id    book            paper
1     harry potter    post it

Is this even possible?

Answer 1

Simply join the details table twice:

Select m.id, d1.name as book, d2.name as paper from main_table m 
join Details_table d1 on m.id =d1.id and d1.type = 'book'
join Details_table d2 on m.id =d2.id and d2.type = 'paper'

Answer 2

Your expected output suggests that you want to pivot the type and generate columns based on its value. Assuming the only types which can appear are book and paper , then the following query should work:

SELECT t2.id,
       MAX(CASE WHEN t2.type = 'book'  THEN name ELSE NULL END) AS book,
       MAX(CASE WHEN t2.type = 'paper' THEN name ELSE NULL END) AS paper
FROM main_table t1
INNER JOIN details_table t2
    ON t1.id = t2.id
GROUP BY t2.id

Demo here:

SQLFiddle