问题描述：
ActorDirector 表：
+-------------+---------+
| Column Name | Type |
+-------------+---------+
| actor_id | int |
| director_id | int |
| timestamp | int |
+-------------+---------+
timestamp 是这张表的主键.
写一条SQL查询语句获取合作过至少三次的演员和导演的 id 对 (actor_id, director_id)
示例：
ActorDirector 表：
+-------------+-------------+-------------+
| actor_id | director_id | timestamp |
+-------------+-------------+-------------+
| 1 | 1 | 0 |
| 1 | 1 | 1 |
| 1 | 1 | 2 |
| 1 | 2 | 3 |
| 1 | 2 | 4 |
| 2 | 1 | 5 |
| 2 | 1 | 6 |
+-------------+-------------+-------------+
Result 表：
+-------------+-------------+
| actor_id | director_id |
+-------------+-------------+
| 1 | 1 |
+-------------+-------------+
唯一的 id 对是 (1, 1)，他们恰好合作了 3 次。
表的DDL：
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for actordirector
-- ----------------------------
DROP TABLE IF EXISTS `actordirector`;
CREATE TABLE `actordirector` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`actor_id` int(255) DEFAULT NULL,
`director_id` int(11) DEFAULT NULL,
`timestamp` datetime(0) DEFAULT NULL,
PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;
-- ----------------------------
-- Records of actordirector
-- ----------------------------
INSERT INTO `actordirector` VALUES (1, 1, 1, '2021-09-23 11:26:34');
INSERT INTO `actordirector` VALUES (2, 1, 1, NULL);
INSERT INTO `actordirector` VALUES (3, 1, 1, NULL);
INSERT INTO `actordirector` VALUES (4, 1, 2, NULL);
INSERT INTO `actordirector` VALUES (5, 1, 2, NULL);
INSERT INTO `actordirector` VALUES (6, 2, 1, NULL);
INSERT INTO `actordirector` VALUES (7, 2, 1, NULL);
SET FOREIGN_KEY_CHECKS = 1;
思路：分组，注意group by可以对多个字段使用。
sql语句，拿去即可运行：
select * from actordirector GROUP BY director_id,actor_id having COUNT(*)>=3运行结果：
我要刷100道算法题，第59道