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数据库系统原理与应用教程（067）—— MySQL 练习题：操作题 82-89（十一）：数据的增、删、改操作
2022-07-30 17:26:00 【睿思达DBA_WGX】
数据库系统原理与应用教程（067）—— MySQL 练习题：操作题 82-89（十一）：数据的增、删、改操作
82、插入数据记录（1）
数据表：exam_record，表结构如下：
| Filed | Type | Null | Key | Extra | Default | Comment |
|---|---|---|---|---|---|---|
| id | int(11) | NO | PRI | auto_increment | (NULL) | 自增ID |
| uid | int(11) | NO | (NULL) | 用户ID | ||
| exam_id | int(11) | NO | (NULL) | 试卷ID | ||
| start_time | datetime | NO | (NULL) | 开始时间 | ||
| submit_time | datetime | YES | (NULL) | 提交时间 | ||
| score | tinyint(4) | YES | (NULL) | 得分 |
现有两个用户的答题记录详情如下：
（1）用户 1001 在 2021 年 9 月 1 日晚上 10 点 11 分 12 秒开始作答试卷 9001，并在 50 分钟后提交，得了 90 分；
（2）用户 1002 在 2021 年 9 月 4 日上午 7 点 1 分 2 秒开始作答试卷 9002，并在 10 分钟后退出了平台。
表 exam_record 的结构：
/* drop table if EXISTS exam_record; CREATE TABLE IF NOT EXISTS exam_record ( id int PRIMARY KEY AUTO_INCREMENT COMMENT '自增ID', uid int NOT NULL COMMENT '用户ID', exam_id int NOT NULL COMMENT '试卷ID', start_time datetime NOT NULL COMMENT '开始时间', submit_time datetime COMMENT '提交时间', score tinyint COMMENT '得分' )CHARACTER SET utf8 COLLATE utf8_general_ci; */
解答：
/* insert into exam_record(uid, exam_id, start_time, submit_time, score) values(1001, 9001, '2021-9-1 22:11:12', '2021-9-1 23:01:12', 90); insert into exam_record(uid, exam_id, start_time, submit_time, score) values(1002, 9002, '2021-9-4 7:1:2', '2021-9-4 7:11:2', null); */
mysql> insert into exam_record(uid, exam_id, start_time, submit_time, score)
-> values(1001, 9001, '2021-9-1 22:11:12', '2021-9-1 23:01:12', 90);
:11:2', null);Query OK, 1 row affected (0.00 sec) mysql> insert into exam_record(uid, exam_id, start_time, submit_time, score) -> values(1002, 9002, '2021-9-4 7:1:2', '2021-9-4 7:11:2', null);
Query OK, 1 row affected (0.00 sec)
mysql> select * from exam_record;
+----+------+---------+---------------------+---------------------+-------+
| id | uid | exam_id | start_time | submit_time | score |
+----+------+---------+---------------------+---------------------+-------+
| 1 | 1001 | 9001 | 2021-09-01 22:11:12 | 2021-09-01 23:01:12 | 90 |
| 2 | 1002 | 9002 | 2021-09-04 07:01:02 | 2021-09-04 07:11:02 | NULL |
+----+------+---------+---------------------+---------------------+-------+
2 rows in set (0.00 sec)
83、插入数据记录（2）
数据表：exam_record，结构如下。
| Filed | Type | Null | Key | Extra | Default | Comment |
|---|---|---|---|---|---|---|
| id | int(11) | NO | PRI | auto_increment | (NULL) | 自增ID |
| uid | int(11) | NO | (NULL) | 用户ID | ||
| exam_id | int(11) | NO | (NULL) | 试卷ID | ||
| start_time | datetime | NO | (NULL) | 开始时间 | ||
| submit_time | datetime | YES | (NULL) | 提交时间 | ||
| score | tinyint(4) | YES | (NULL) | 得分 |
表 exam_record 中包含多年来用户作答试卷记录。创建一张新表 exam_record_before_2021（表结构和 exam_record 表一致） 用来备份 2021 年之前的试题作答记录，请将 2021 年之前的已完成了的试题作答纪录导入到该表。
表结构及数据如下：
/* drop table if EXISTS exam_record; CREATE TABLE IF NOT EXISTS exam_record ( id int PRIMARY KEY AUTO_INCREMENT COMMENT '自增ID', uid int NOT NULL COMMENT '用户ID', exam_id int NOT NULL COMMENT '试卷ID', start_time datetime NOT NULL COMMENT '开始时间', submit_time datetime COMMENT '提交时间', score tinyint COMMENT '得分' )CHARACTER SET utf8 COLLATE utf8_general_ci; drop table if EXISTS exam_record_before_2021; CREATE TABLE IF NOT EXISTS exam_record_before_2021 ( id int PRIMARY KEY AUTO_INCREMENT COMMENT '自增ID', uid int NOT NULL COMMENT '用户ID', exam_id int NOT NULL COMMENT '试卷ID', start_time datetime NOT NULL COMMENT '开始时间', submit_time datetime COMMENT '提交时间', score tinyint COMMENT '得分' )CHARACTER SET utf8 COLLATE utf8_general_ci; INSERT INTO exam_record(uid,exam_id,start_time,submit_time,score) VALUES (1001, 9001, '2020-01-01 09:00:01', null, null), (1001, 9002, '2020-01-02 09:01:01', '2020-01-02 09:21:01', 70), (1001, 9002, '2020-09-02 09:00:01', null, null), (1002, 9001, '2021-05-02 10:01:01', '2021-05-02 10:30:01', 81), (1002, 9002, '2021-09-02 12:01:01', null, null); */
解答：
/* insert into exam_record_before_2021 select * from exam_record where start_time <= '2021-1-1' and submit_time is not null; */
mysql> select * from exam_record_before_2021;
+----+------+---------+---------------------+---------------------+-------+
| id | uid | exam_id | start_time | submit_time | score |
+----+------+---------+---------------------+---------------------+-------+
| 2 | 1001 | 9002 | 2020-01-02 09:01:01 | 2020-01-02 09:21:01 | 70 |
+----+------+---------+---------------------+---------------------+-------+
1 row in set (0.00 sec)
84、插入数据记录（3）
试题信息表：examination_info，表结构如下：
| Filed | Type | Null | Key | Extra | Default | Comment |
|---|---|---|---|---|---|---|
| id | int(11) | NO | PRI | auto_increment | (NULL) | 自增ID |
| exam_id | int(11) | NO | UNI | (NULL) | 试卷ID | |
| tag | varchar(32) | YES | (NULL) | 类别标签 | ||
| difficulty | varchar(8) | YES | (NULL) | 难度 | ||
| duration | int(11) | NO | (NULL) | 时长(分钟数) | ||
| release_time | datetime | YES | (NULL) | 发布时间 |
现有一套 ID 为 9003 的高难度 SQL 试卷，时长为一个半小时，请将 2021-01-01 00:00:00 作为发布时间插入到试题信息表（examination_info），不管该 ID 试卷是否存在，都要插入成功。
表结构及数据如下：
/* drop table if EXISTS examination_info; CREATE TABLE IF NOT EXISTS examination_info ( id int PRIMARY KEY AUTO_INCREMENT COMMENT '自增ID', exam_id int UNIQUE NOT NULL COMMENT '试卷ID', tag varchar(32) COMMENT '类别标签', difficulty varchar(8) COMMENT '难度', duration int NOT NULL COMMENT '时长(分钟数)', release_time datetime COMMENT '发布时间' )CHARACTER SET utf8 COLLATE utf8_bin; TRUNCATE examination_info; INSERT INTO examination_info(exam_id,tag,difficulty,duration,release_time) VALUES (9001, 'SQL', 'hard', 60, '2020-01-01 10:00:00'), (9002, '算法', 'easy', 60, '2020-01-01 10:00:00'), (9003, 'SQL', 'medium', 60, '2020-01-02 10:00:00'), (9004, '算法', 'hard', 80, '2020-01-01 10:00:00'); */
mysql> select * from examination_info;
+----+---------+--------+------------+----------+---------------------+
| id | exam_id | tag | difficulty | duration | release_time |
+----+---------+--------+------------+----------+---------------------+
| 1 | 9001 | SQL | hard | 60 | 2020-01-01 10:00:00 |
| 2 | 9002 | 算法 | easy | 60 | 2020-01-01 10:00:00 |
| 3 | 9003 | SQL | medium | 60 | 2020-01-02 10:00:00 |
| 4 | 9004 | 算法 | hard | 80 | 2020-01-01 10:00:00 |
+----+---------+--------+------------+----------+---------------------+
4 rows in set (0.00 sec)
解答：
/* replace into examination_info(exam_id, tag, difficulty, duration, release_time) values(9003, 'SQL', 'hard', 90, '2021-01-01 00:00:00'); */
mysql> replace into examination_info(exam_id, tag, difficulty, duration, release_time)
-> values(9003, 'SQL', 'hard', 90, '2021-01-01 00:00:00');
Query OK, 2 rows affected (0.00 sec)
mysql> select * from examination_info;
+----+---------+--------+------------+----------+---------------------+
| id | exam_id | tag | difficulty | duration | release_time |
+----+---------+--------+------------+----------+---------------------+
| 1 | 9001 | SQL | hard | 60 | 2020-01-01 10:00:00 |
| 2 | 9002 | 算法 | easy | 60 | 2020-01-01 10:00:00 |
| 4 | 9004 | 算法 | hard | 80 | 2020-01-01 10:00:00 |
| 5 | 9003 | SQL | hard | 90 | 2021-01-01 00:00:00 |
+----+---------+--------+------------+----------+---------------------+
4 rows in set (0.00 sec)
85、更新数据记录（1）
现有一张试卷信息表：examination_info，表结构如下：
| Filed | Type | Null | Key | Extra | Default | Comment |
|---|---|---|---|---|---|---|
| id | int(11) | NO | PRI | auto_increment | (NULL) | 自增ID |
| exam_id | int(11) | NO | UNI | (NULL) | 试卷ID | |
| tag | char(32) | YES | (NULL) | 类别标签 | ||
| difficulty | char(8) | YES | (NULL) | 难度 | ||
| duration | int(11) | NO | (NULL) | 时长 | ||
| release_time | datetime | YES | (NULL) | 发布时间 |
请把 examination_info 表中 tag 列为【PYTHON】的数据全部修改为【Python】。
表结构及数据如下：
/* drop table if EXISTS examination_info; CREATE TABLE IF NOT EXISTS examination_info ( id int PRIMARY KEY AUTO_INCREMENT COMMENT '自增ID', exam_id int UNIQUE NOT NULL COMMENT '试卷ID', tag varchar(32) COMMENT '类别标签', difficulty varchar(8) COMMENT '难度', duration int NOT NULL COMMENT '时长', release_time datetime COMMENT '发布时间' )CHARACTER SET utf8 COLLATE utf8_bin; TRUNCATE examination_info; INSERT INTO examination_info(exam_id,tag,difficulty,duration,release_time) VALUES (9001, 'SQL', 'hard', 60, '2020-01-01 10:00:00'), (9002, 'python', 'easy', 60, '2020-01-01 10:00:00'), (9003, 'Python', 'medium', 80, '2020-01-01 10:00:00'), (9004, 'PYTHON', 'hard', 80, '2020-01-01 10:00:00'); */
解答：
mysql> select * from examination_info;
+----+---------+--------+------------+----------+---------------------+
| id | exam_id | tag | difficulty | duration | release_time |
+----+---------+--------+------------+----------+---------------------+
| 1 | 9001 | SQL | hard | 60 | 2020-01-01 10:00:00 |
| 2 | 9002 | python | easy | 60 | 2020-01-01 10:00:00 |
| 3 | 9003 | Python | medium | 80 | 2020-01-01 10:00:00 |
| 4 | 9004 | PYTHON | hard | 80 | 2020-01-01 10:00:00 |
+----+---------+--------+------------+----------+---------------------+
4 rows in set (0.00 sec)
mysql> update examination_info set tag = 'Python' where tag = 'PYTHON';
Query OK, 1 row affected (0.06 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from examination_info;
+----+---------+--------+------------+----------+---------------------+
| id | exam_id | tag | difficulty | duration | release_time |
+----+---------+--------+------------+----------+---------------------+
| 1 | 9001 | SQL | hard | 60 | 2020-01-01 10:00:00 |
| 2 | 9002 | python | easy | 60 | 2020-01-01 10:00:00 |
| 3 | 9003 | Python | medium | 80 | 2020-01-01 10:00:00 |
| 4 | 9004 | Python | hard | 80 | 2020-01-01 10:00:00 |
+----+---------+--------+------------+----------+---------------------+
4 rows in set (0.00 sec)
86、更新数据记录（2）
现有一张试卷答题记录表：exam_record，表结构如下：
| Filed | Type | Null | Key | Extra | Default | Comment |
|---|---|---|---|---|---|---|
| id | int(11) | NO | PRI | auto_increment | (NULL) | 自增ID |
| uid | int(11) | NO | (NULL) | 用户ID | ||
| exam_id | int(11) | NO | (NULL) | 试卷ID | ||
| start_time | datetime | NO | (NULL) | 开始时间 | ||
| submit_time | datetime | YES | (NULL) | 提交时间 | ||
| score | tinyint(4) | YES | (NULL) | 得分 |
其中包含多年来的用户答题记录，请把 exam_record 表中 2021 年 9 月 1 日之前开始作答的未完成记录全部改为被动完成。即：将完成时间改为 ‘2099-01-01 00:00:00’，分数改为 0。
表结构及数据如下：
/* drop table if EXISTS exam_record; CREATE TABLE IF NOT EXISTS exam_record ( id int PRIMARY KEY AUTO_INCREMENT COMMENT '自增ID', uid int NOT NULL COMMENT '用户ID', exam_id int NOT NULL COMMENT '试卷ID', start_time datetime NOT NULL COMMENT '开始时间', submit_time datetime COMMENT '提交时间', score tinyint COMMENT '得分' )CHARACTER SET utf8 COLLATE utf8_general_ci; INSERT INTO exam_record(uid,exam_id,start_time,submit_time,score) VALUES (1001, 9001, '2020-01-02 09:01:01', '2020-01-02 09:21:01', 80), (1001, 9002, '2021-09-01 09:01:01', '2021-09-01 09:21:01', 90), (1002, 9001, '2021-08-02 19:01:01', null, null), (1002, 9002, '2021-09-05 19:01:01', '2021-09-05 19:40:01', 89), (1003, 9001, '2021-09-02 12:01:01', null, null), (1003, 9002, '2021-09-01 12:01:01', null, null); */
解答：
mysql> select * from exam_record;
+----+------+---------+---------------------+---------------------+-------+
| id | uid | exam_id | start_time | submit_time | score |
+----+------+---------+---------------------+---------------------+-------+
| 1 | 1001 | 9001 | 2020-01-02 09:01:01 | 2020-01-02 09:21:01 | 80 |
| 2 | 1001 | 9002 | 2021-09-01 09:01:01 | 2021-09-01 09:21:01 | 90 |
| 3 | 1002 | 9001 | 2021-08-02 19:01:01 | NULL | NULL |
| 4 | 1002 | 9002 | 2021-09-05 19:01:01 | 2021-09-05 19:40:01 | 89 |
| 5 | 1003 | 9001 | 2021-09-02 12:01:01 | NULL | NULL |
| 6 | 1003 | 9002 | 2021-09-01 12:01:01 | NULL | NULL |
+----+------+---------+---------------------+---------------------+-------+
6 rows in set (0.00 sec)
/* update exam_record set submit_time = '2099-01-01 0:0:0', score = 0 where start_time < '2021-9-1 0:0:0' and submit_time is null; */
mysql> update exam_record set submit_time = '2099-01-01 0:0:0', score = 0
-> where start_time < '2021-9-1 0:0:0' and submit_time is null;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from exam_record;
+----+------+---------+---------------------+---------------------+-------+
| id | uid | exam_id | start_time | submit_time | score |
+----+------+---------+---------------------+---------------------+-------+
| 1 | 1001 | 9001 | 2020-01-02 09:01:01 | 2020-01-02 09:21:01 | 80 |
| 2 | 1001 | 9002 | 2021-09-01 09:01:01 | 2021-09-01 09:21:01 | 90 |
| 3 | 1002 | 9001 | 2021-08-02 19:01:01 | 2099-01-01 00:00:00 | 0 |
| 4 | 1002 | 9002 | 2021-09-05 19:01:01 | 2021-09-05 19:40:01 | 89 |
| 5 | 1003 | 9001 | 2021-09-02 12:01:01 | NULL | NULL |
| 6 | 1003 | 9002 | 2021-09-01 12:01:01 | NULL | NULL |
+----+------+---------+---------------------+---------------------+-------+
6 rows in set (0.00 sec)
87、删除记录（1）
现有一张试卷答题记录表：exam_record，表结构如下表：
| Filed | Type | Null | Key | Extra | Default | Comment |
|---|---|---|---|---|---|---|
| id | int(11) | NO | PRI | auto_increment | (NULL) | 自增ID |
| uid | int(11) | NO | (NULL) | 用户ID | ||
| exam_id | int(11) | NO | (NULL) | 试卷ID | ||
| start_time | datetime | NO | (NULL) | 开始时间 | ||
| submit_time | datetime | YES | (NULL) | 提交时间 | ||
| score | tinyint(4) | YES | (NULL) | 得分 |
【问题】请删除 exam_record 表中答题时间小于 5 分钟整且分数不及格（及格线为60分）的记录；
表结构及数据如下：
/* drop table if EXISTS exam_record; CREATE TABLE IF NOT EXISTS exam_record ( id int PRIMARY KEY AUTO_INCREMENT COMMENT '自增ID', uid int NOT NULL COMMENT '用户ID', exam_id int NOT NULL COMMENT '试卷ID', start_time datetime NOT NULL COMMENT '开始时间', submit_time datetime COMMENT '提交时间', score tinyint COMMENT '得分' )CHARACTER SET utf8 COLLATE utf8_general_ci; TRUNCATE exam_record; INSERT INTO exam_record(uid, exam_id, start_time, submit_time, score) VALUES (1001, 9001, '2020-01-01 22:11:12', '2020-01-01 23:16:12', 50), (1001, 9002, '2020-01-02 09:01:01', '2020-01-02 09:06:00', 58), (1002, 9001, '2021-05-02 10:01:01', '2021-05-02 10:05:58', 60), (1002, 9002, '2021-06-02 19:01:01', '2021-06-02 19:05:01', 54), (1003, 9001, '2021-09-05 19:01:01', '2021-09-05 19:40:01', 49), (1003, 9001, '2021-09-05 19:01:01', '2021-09-05 19:15:01', 70), (1003, 9001, '2021-09-06 19:01:01', '2021-09-06 19:05:01', 80), (1003, 9002, '2021-09-09 07:01:02', null, null); */
解答：
mysql> select * from exam_record;
+----+------+---------+---------------------+---------------------+-------+
| id | uid | exam_id | start_time | submit_time | score |
+----+------+---------+---------------------+---------------------+-------+
| 1 | 1001 | 9001 | 2020-01-01 22:11:12 | 2020-01-01 23:16:12 | 50 |
| 2 | 1001 | 9002 | 2020-01-02 09:01:01 | 2020-01-02 09:06:00 | 58 |
| 3 | 1002 | 9001 | 2021-05-02 10:01:01 | 2021-05-02 10:05:58 | 60 |
| 4 | 1002 | 9002 | 2021-06-02 19:01:01 | 2021-06-02 19:05:01 | 54 |
| 5 | 1003 | 9001 | 2021-09-05 19:01:01 | 2021-09-05 19:40:01 | 49 |
| 6 | 1003 | 9001 | 2021-09-05 19:01:01 | 2021-09-05 19:15:01 | 70 |
| 7 | 1003 | 9001 | 2021-09-06 19:01:01 | 2021-09-06 19:05:01 | 80 |
| 8 | 1003 | 9002 | 2021-09-09 07:01:02 | NULL | NULL |
+----+------+---------+---------------------+---------------------+-------+
8 rows in set (0.00 sec)
/* delete from exam_record where timediff(submit_time, start_time) < '00:05:00' and score < 60 or submit_time is null; */
mysql> delete from exam_record
-> where timediff(submit_time, start_time) < '00:05:00' and score < 60 or submit_time is null;
Query OK, 3 rows affected (0.00 sec)
mysql> select * from exam_record;
+----+------+---------+---------------------+---------------------+-------+
| id | uid | exam_id | start_time | submit_time | score |
+----+------+---------+---------------------+---------------------+-------+
| 1 | 1001 | 9001 | 2020-01-01 22:11:12 | 2020-01-01 23:16:12 | 50 |
| 3 | 1002 | 9001 | 2021-05-02 10:01:01 | 2021-05-02 10:05:58 | 60 |
| 5 | 1003 | 9001 | 2021-09-05 19:01:01 | 2021-09-05 19:40:01 | 49 |
| 6 | 1003 | 9001 | 2021-09-05 19:01:01 | 2021-09-05 19:15:01 | 70 |
| 7 | 1003 | 9001 | 2021-09-06 19:01:01 | 2021-09-06 19:05:01 | 80 |
+----+------+---------+---------------------+---------------------+-------+
5 rows in set (0.00 sec)
88、删除记录（2）
现有一张试卷答题记录表：exam_record，表结构如下表：
| Filed | Type | Null | Key | Extra | Default | Comment |
|---|---|---|---|---|---|---|
| id | int(11) | NO | PRI | auto_increment | (NULL) | 自增ID |
| uid | int(11) | NO | (NULL) | 用户ID | ||
| exam_id | int(11) | NO | (NULL) | 试卷ID | ||
| start_time | datetime | NO | (NULL) | 开始时间 | ||
| submit_time | datetime | YES | (NULL) | 提交时间 | ||
| score | tinyint(4) | YES | (NULL) | 得分 |
【问题】请删除 exam_record 表中未完成作答或作答时间小于 5 分钟整的记录中，开始作答时间最早的 3 条记录。
表结构及数据如下：
/* drop table if EXISTS exam_record; CREATE TABLE IF NOT EXISTS exam_record ( id int PRIMARY KEY AUTO_INCREMENT COMMENT '自增ID', uid int NOT NULL COMMENT '用户ID', exam_id int NOT NULL COMMENT '试卷ID', start_time datetime NOT NULL COMMENT '开始时间', submit_time datetime COMMENT '提交时间', score tinyint COMMENT '得分' )CHARACTER SET utf8 COLLATE utf8_general_ci; TRUNCATE exam_record; INSERT INTO exam_record(uid, exam_id, start_time, submit_time, score) VALUES (1001, 9001, '2020-01-01 22:11:12', '2020-01-01 23:16:12', 50), (1001, 9002, '2020-01-02 09:01:01', '2020-01-02 09:06:00', 58), (1001, 9002, '2020-01-02 09:01:01', '2020-01-02 09:05:01', 58), (1002, 9001, '2021-05-02 10:01:01', '2021-05-02 10:06:58', 60), (1002, 9002, '2021-06-02 19:01:01', null, null), (1003, 9001, '2021-09-05 19:01:01', null, null), (1003, 9001, '2021-09-05 19:01:01', null, null), (1003, 9002, '2021-09-09 07:01:02', null, null); */
解答：
mysql> select * from exam_record;
+----+------+---------+---------------------+---------------------+-------+
| id | uid | exam_id | start_time | submit_time | score |
+----+------+---------+---------------------+---------------------+-------+
| 1 | 1001 | 9001 | 2020-01-01 22:11:12 | 2020-01-01 23:16:12 | 50 |
| 2 | 1001 | 9002 | 2020-01-02 09:01:01 | 2020-01-02 09:06:00 | 58 |
| 3 | 1001 | 9002 | 2020-01-02 09:01:01 | 2020-01-02 09:05:01 | 58 |
| 4 | 1002 | 9001 | 2021-05-02 10:01:01 | 2021-05-02 10:06:58 | 60 |
| 5 | 1002 | 9002 | 2021-06-02 19:01:01 | NULL | NULL |
| 6 | 1003 | 9001 | 2021-09-05 19:01:01 | NULL | NULL |
| 7 | 1003 | 9001 | 2021-09-05 19:01:01 | NULL | NULL |
| 8 | 1003 | 9002 | 2021-09-09 07:01:02 | NULL | NULL |
+----+------+---------+---------------------+---------------------+-------+
8 rows in set (0.00 sec)
/* delete from exam_record where timediff(submit_time, start_time) < '00:05:00' or submit_time is null order by start_time limit 3; */
mysql> delete from exam_record
-> where timediff(submit_time, start_time) < '00:05:00' or submit_time is null
-> order by start_time limit 3;
Query OK, 3 rows affected (0.00 sec)
mysql> select * from exam_record;
+----+------+---------+---------------------+---------------------+-------+
| id | uid | exam_id | start_time | submit_time | score |
+----+------+---------+---------------------+---------------------+-------+
| 1 | 1001 | 9001 | 2020-01-01 22:11:12 | 2020-01-01 23:16:12 | 50 |
| 4 | 1002 | 9001 | 2021-05-02 10:01:01 | 2021-05-02 10:06:58 | 60 |
| 6 | 1003 | 9001 | 2021-09-05 19:01:01 | NULL | NULL |
| 7 | 1003 | 9001 | 2021-09-05 19:01:01 | NULL | NULL |
| 8 | 1003 | 9002 | 2021-09-09 07:01:02 | NULL | NULL |
+----+------+---------+---------------------+---------------------+-------+
5 rows in set (0.00 sec)
89、删除记录（3）
现有一张试卷答题记录表：exam_record，表结构如下表：
| Filed | Type | Null | Key | Extra | Default | Comment |
|---|---|---|---|---|---|---|
| id | int(11) | NO | PRI | auto_increment | (NULL) | 自增ID |
| uid | int(11) | NO | (NULL) | 用户ID | ||
| exam_id | int(11) | NO | (NULL) | 试卷ID | ||
| start_time | datetime | NO | (NULL) | 开始时间 | ||
| submit_time | datetime | YES | (NULL) | 提交时间 | ||
| score | tinyint(4) | YES | (NULL) | 得分 |
【问题】请删除 exam_record 表中所有记录，并重置自增主键。
表结构及数据如下：
/* drop table if EXISTS exam_record; CREATE TABLE IF NOT EXISTS exam_record ( id int PRIMARY KEY AUTO_INCREMENT COMMENT '自增ID', uid int NOT NULL COMMENT '用户ID', exam_id int NOT NULL COMMENT '试卷ID', start_time datetime NOT NULL COMMENT '开始时间', submit_time datetime COMMENT '提交时间', score tinyint COMMENT '得分' )CHARACTER SET utf8 COLLATE utf8_general_ci; TRUNCATE exam_record; INSERT INTO exam_record(uid, exam_id, start_time, submit_time, score) VALUES (1001, 9001, '2020-01-01 22:11:12', '2020-01-01 23:16:12', 50), (1001, 9002, '2020-01-02 09:01:01', '2020-01-02 09:06:00', 58); */
解答：
mysql> select * from exam_record;
+----+------+---------+---------------------+---------------------+-------+
| id | uid | exam_id | start_time | submit_time | score |
+----+------+---------+---------------------+---------------------+-------+
| 1 | 1001 | 9001 | 2020-01-01 22:11:12 | 2020-01-01 23:16:12 | 50 |
| 2 | 1001 | 9002 | 2020-01-02 09:01:01 | 2020-01-02 09:06:00 | 58 |
+----+------+---------+---------------------+---------------------+-------+
2 rows in set (0.00 sec)
mysql> truncate table exam_record;
Query OK, 0 rows affected (0.01 sec)
mysql> truncate table exam_record;
Query OK, 0 rows affected (0.01 sec)
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