这篇文章将为大家详细讲解有关如何使用mysqldump备份，小编觉得挺实用的，因此分享给大家做个参考，希望大家阅读完这篇文章后可以有所收获。
问题描述
在一次使用mysqldump备份单表部分数据时，发现无备份数据。阵针对这一奇怪现象，进行分析。
问题复现与分析
#表结构信息
mysql> show create table test.t1;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t1 | CREATE TABLE `t1` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`id`),
KEY `idx_t` (`time`)
) ENGINE=InnoDB AUTO_INCREMENT=16 DEFAULT CHARSET=utf8 |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
#表数据信息
mysql> select * from test.t1;
+----+---------------------+
| id | time |
+----+---------------------+
| 1 | 2018-12-10 22:15:39 |
| 2 | 2018-12-10 22:15:47 |
| 3 | 2018-12-10 22:15:50 |
| 4 | 2018-12-10 22:15:56 |
| 5 | 2018-12-10 22:15:57 |
| 6 | 2018-12-10 22:15:58 |
| 7 | 2018-12-10 22:15:58 |
| 8 | 2018-12-10 22:16:06 |
| 9 | 2018-12-10 22:16:06 |
| 10 | 2018-12-10 22:16:07 |
| 11 | 2018-12-10 22:16:08 |
| 12 | 2018-12-10 22:16:13 |
| 13 | 2018-12-10 22:16:13 |
| 14 | 2018-12-10 22:16:14 |
| 15 | 2018-12-10 22:16:15 |
+----+---------------------+
15 rows in set (0.00 sec)使用mysqldump --where选项备份t1表部分数据。
#使用mysqldump根据time列条件备份
mysqldump -uroot -p123456 --default-character-set=utf8 -q --master-data=2 --single-transaction --databases test --tables t1 --where "time>'2018-12-10 22:16:08'">beifen.sql
#通过备份文件可以看出备份结果中并无数据。
...
LOCK TABLES `t1` WRITE;
;
;
UNLOCK TABLES;
...在MySQL中使用相同条件查询，并无异常，可以查到数据。
[root@master ~]# mysql -uroot -p123456 -e "select * from test.t1 where time>'2018-12-10 22:16:08'"
mysql: [Warning] Using a password on the command line interface can be insecure.
+----+---------------------+
| id | time |
+----+---------------------+
| 12 | 2018-12-10 22:16:13 |
| 13 | 2018-12-10 22:16:13 |
| 14 | 2018-12-10 22:16:14 |
| 15 | 2018-12-10 22:16:15 |
+----+---------------------+尝试备份t1全表数据
mysqldump -uroot -p123456 --default-character-set=utf8 -q --master-data=2 --single-transaction --databases test --tables t1 >beifen.sql
#有数据，但是仔细对照，我们可以发现时间回退了八个小时。
LOCK TABLES `t1` WRITE;
;
INSERT INTO `t1` VALUES (1,'2018-12-10 14:15:39'),(2,'2018-12-10 14:15:47'),(3,'2018-12-10 14:15:50'),(4,'2018-12-10 14:15:56'),(5,'2018-12-10 14:15:57'),(6,'2018-12-10 14:15:58'),(7,'2018-12-10 14:15:58'),(8,'2018-12-10 14:16:06'),(9,'2018-12-10 14:16:06'),(10,'2018-12-10 14:16:07'),(11,'2018-12-10 14:16:08'),(12,'2018-12-10 14:16:13'),(13,'2018-12-10 14:16:13'),(14,'2018-12-10 14:16:14'),(15,'2018-12-10 14:16:15');
;
UNLOCK TABLES;
#查看mysqldump备份文件头部信息，mysqldump使用的是中时区。
...
;
...
#查看MySQL和系统时区。
mysql> show variables like '%time%';
+---------------------------------+-------------------+
| Variable_name | Value |
+---------------------------------+-------------------+
| binlog_max_flush_queue_time | 0 |
| connect_timeout | 10 |
| datetime_format | %Y-%m-%d %H:%i:%s |
| default_password_lifetime | 0 |
| delayed_insert_timeout | 300 |
| explicit_defaults_for_timestamp | OFF |
| flush_time | 0 |
| have_statement_timeout | YES |
| innodb_flush_log_at_timeout | 1 |
| innodb_lock_wait_timeout | 50 |
| innodb_old_blocks_time | 1000 |
| innodb_rollback_on_timeout | OFF |
| interactive_timeout | 28800 |
| lc_time_names | en_US |
| lock_wait_timeout | 31536000 |
| log_timestamps | UTC |
| long_query_time | 10.000000 |
| max_execution_time | 0 |
| net_read_timeout | 30 |
| net_write_timeout | 60 |
| rpl_semi_sync_master_timeout | 10000 |
| rpl_stop_slave_timeout | 31536000 |
| slave_net_timeout | 60 |
| slow_launch_time | 2 |
| system_time_zone | CST |
| time_format | %H:%i:%s |
| time_zone | +08:00 |
| timestamp | 1544775697.554299 |
| wait_timeout | 28800 |
+---------------------------------+-------------------+
29 rows in set (0.01 sec)
[root@master ~]# date -R
Wed, 12 Dec 2018 16:00:34 +0800
#模拟数据恢复
mysql> drop table test.t1;
mysql -uroot -p123456<beifen
mysql> select * from t1;
+----+---------------------+
| id | time |
+----+---------------------+
| 1 | 2018-12-10 22:15:39 |
| 2 | 2018-12-10 22:15:47 |
| 3 | 2018-12-10 22:15:50 |
| 4 | 2018-12-10 22:15:56 |
| 5 | 2018-12-10 22:15:57 |
| 6 | 2018-12-10 22:15:58 |
| 7 | 2018-12-10 22:15:58 |
| 8 | 2018-12-10 22:16:06 |
| 9 | 2018-12-10 22:16:06 |
| 10 | 2018-12-10 22:16:07 |
| 11 | 2018-12-10 22:16:08 |
| 12 | 2018-12-10 22:16:13 |
| 13 | 2018-12-10 22:16:13 |
| 14 | 2018-12-10 22:16:14 |
| 15 | 2018-12-10 22:16:15 |
+----+---------------------+
15 rows in set (0.00 sec)
#数据恢复正常。但是存在一个问题，因为mysqldump备份时会把数据进行时区转换，导致mysqldump过滤条件与筛选的数据差8个小时，所以可能会使where条件过滤不准确。比如文章开头所碰到的问题。解决办法
#使用--skip-tz-utc，不使用mysqldump默认的中时区。
mysqldump --default-character-set=utf8 -q --master-data=2 --single-transaction --databases test --tables t1 --where "time='2018-12-10 22:16:08'" -uroot -p123456 --skip-tz-utc>beifen.sql
#数据完全正确，文件头部无时区转换，所以数据恢复时正常。
LOCK TABLES `t1` WRITE;
;
INSERT INTO `t1` VALUES (11,'2018-12-10 22:16:08');
;
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