[英]MySQL one-to-many relationship single query
我有这两个表。 我将使其尽可能简单:
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
我需要的结果是使用这两种类型的名称获取ID。
id book paper
1 harry potter post it
这有可能吗?
只需将详细信息表连接两次:
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'
预期的输出表明您希望透视该type
并根据其值生成列。 假设可以出现的唯一类型是book
和paper
,那么以下查询应该起作用:
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
演示在这里:
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