Php mysql连接：获取每种类型的部件数量

我有两张桌子：

1） 零件

2） 职位

在posts表中，post有三种类型之一，因此在type列I中输入值（1、2或3）

我想得到这样的表（包括count和join）

part_id | part_name | count_posts_type1 | count_posts_type2 | count_posts_type3

如何使用mysql实现这一点

例如：

---

你有没有尝试过类似（只是开玩笑，我知道你什么都没试过）的东西，比如：

SELECT
     parts.part_id,
     parts.part_name,
     COUNT(t1.post_id) AS count_posts_type1,
     COUNT(t2.post_id) AS  count_posts_type2,
     COUNT(t3.post_id) AS count_posts_type3
FROM posts
     RIGHT JOIN part ON posts.part_id=parts.part_id 
     INNER JOIN ( SELECT post_id FROM posts WHERE type=1 ) as t1(post_id) ON posts.post_id = t1.post_id
     INNER JOIN ( SELECT post_id FROM posts WHERE type=1 ) as t2(post_id) ON posts.post_id = t2.post_id
     INNER JOIN ( SELECT post_id FROM posts WHERE type=1 ) as t3(post_id) ON posts.post_id = t3.post_id

---

如果类型列表有限，则使用sum和case-when是一种相当常见的方法

然后是一个左连接，对没有post的部分有结果（和一个合并，在和上有0而不是null），现在我们开始

select 
pa.part_id, pa.part_name,
coalesce(sum(case when po.type = 1 then 1 else 0 end), 0) as count_posts_type1,
coalesce(sum(case when po.type = 2 then 1 else 0 end), 0) as count_posts_type2,
coalesce(sum(case when po.type = 3 then 1 else 0 end), 0) as count_posts_type3
from parts pa
left join posts po on po.part_id = pa.part_id
group by pa.part_id, pa.part_name

---

这两个表之间的共同点是什么？共同点是part_id I fixed itI为我需要的结果添加了一个示例

SELECT
     parts.part_id,
     parts.part_name,
     COUNT(t1.post_id) AS count_posts_type1,
     COUNT(t2.post_id) AS  count_posts_type2,
     COUNT(t3.post_id) AS count_posts_type3
FROM posts
     RIGHT JOIN part ON posts.part_id=parts.part_id 
     INNER JOIN ( SELECT post_id FROM posts WHERE type=1 ) as t1(post_id) ON posts.post_id = t1.post_id
     INNER JOIN ( SELECT post_id FROM posts WHERE type=1 ) as t2(post_id) ON posts.post_id = t2.post_id
     INNER JOIN ( SELECT post_id FROM posts WHERE type=1 ) as t3(post_id) ON posts.post_id = t3.post_id

select 
pa.part_id, pa.part_name,
coalesce(sum(case when po.type = 1 then 1 else 0 end), 0) as count_posts_type1,
coalesce(sum(case when po.type = 2 then 1 else 0 end), 0) as count_posts_type2,
coalesce(sum(case when po.type = 3 then 1 else 0 end), 0) as count_posts_type3
from parts pa
left join posts po on po.part_id = pa.part_id
group by pa.part_id, pa.part_name