将大量数据分组在一起并创建动态amt列

Question

我有一个这样的mysql数据库：

id - join_id - bool
1 - 32 - 1
2 - 32 - 0
3 - 32 - 1
4 - 32 - 1

我想对此提出疑问：

join_id - bool (- amount)
32 - 1 - 3 (aka there are 3 instances where the join_id and bool are 32 and 1);
32 - 0 - 1 (aka there is 1 instances where the join_id and bool are 32 and 0);

任何关键词或名字都会很有帮助。

Answer 1

我想这就是你要找的东西：

SELECT join_id, bool, COUNT(id) AS amount FROM mytable GROUP BY join_id,bool