sql 多对多关系查询 returns 单条记录

Question

如何得到 project_id，其中 technology_id = 1 和 technology_id = 2 在一行中？

+------------+---------------+
| project_id | technology_id |
+------------+---------------+
|          1 |             1 |
|          1 |             2 |
|          3 |             2 |
|          7 |             1 |
|          9 |             1 |
+------------+---------------+

Answer 1

按 product_id 分组，只取同时具有 technology_id 的那些组

select project_id
from your_table
where technology_id in (1,2)
group by project_id
having count(*) = 2