SQL之group by连接2个以上字段

group by连接1个字段：

1.select后接group by后面的字段

2.顺序：where----group by-----order by------having

3. select 后面的所有列中,没有使用聚合函数的列,必须出现在 group by 后面

group by 后连接2个字段：

一个字段就依据一个条件分组，两个字段就依据两个条件分组。。。。。。

不满足另外分为1组。

力扣刷题：1050合作过至少三次的演员和导演

ActorDirector 表：

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| actor_id    | int     |
| director_id | int     |
| timestamp   | int     |
+-------------+---------+
在 SQL 中，timestamp 是这张表的主键.
查询合作过至少三次的演员和导演的 id 对 (actor_id, director_id）

答案：

select actor_id,director_id from actordirector
group by actor_id,director_id
having count(*)>=3

表结构：

Create table If Not Exists ActorDirector (actor_id int, director_id int, timestamp int)
Truncate table ActorDirector
insert into ActorDirector (actor_id, director_id, timestamp) values ('1', '1', '0')
insert into ActorDirector (actor_id, director_id, timestamp) values ('1', '1', '1')
insert into ActorDirector (actor_id, director_id, timestamp) values ('1', '1', '2')
insert into ActorDirector (actor_id, director_id, timestamp) values ('1', '2', '3')
insert into ActorDirector (actor_id, director_id, timestamp) values ('1', '2', '4')
insert into ActorDirector (actor_id, director_id, timestamp) values ('2', '1', '5')
insert into ActorDirector (actor_id, director_id, timestamp) values ('2', '1', '6')