MySQL如何恢复单库或单表,以及可能遇到的坑

前言：

MySQL 逻辑备份工具最常用的就是 mysqldump 了，一般我们都是备份整个实例或部分业务库。不清楚你有没有做过恢复，恢复场景可能就比较多了，比如我想恢复某个库或某个表等。那么如何从全备中恢复单库或单表，这其中又有哪些隐藏的坑呢？这篇文章我们一起来看下。

1.如何恢复单库或单表

前面文章有介绍过 MySQL 的备份与恢复。可能我们每个数据库实例中都不止一个库，一般备份都是备份整个实例，但恢复需求又是多种多样的，比如说我想只恢复某个库或某张表，这个时候应该怎么操作呢？

如果你的实例数据量不大，可以在另外一个环境恢复出整个实例，然后再单独备份出所需库或表用来恢复。不过这种方法不够灵活，并且只适用数据量比较少的情况。

其实从全备中恢复单库还是比较方便的，有个 --one-database 参数可以指定单库恢复，下面来具体演示下：

# 查看及备份所有库mysql> show databases;+--------------------+| Database      |+--------------------+| information_schema || mysql       || performance_schema || sbtest       || sys        || testdb       || testdb2      |+--------------------+mysqldump -uroot -pxxxx -R -E --single-transaction --all-databases > all_db.sql# 删除testdb库 并进行单库恢复mysql> drop database testdb;Query OK, 36 rows affected (2.06 sec)# 貌似恢复前 testdb库不存在的话要手动新建mysql -uroot -pxxxx --one-database testdb < all_db.sql

# 从全备中恢复单库sed -n '/^-- Current Database: `testdb`/,/^-- Current Database: `/p' all_db.sql > testdb.sql# 筛选出单表语句cat all_db.sql | sed -e '/./{H;$!d;}' -e 'x;/CREATE TABLE `test_tb`/!d;q' > /tmp/test_tb_info.sql cat all_db.sql | grep --ignore-case 'insert into `test_tb`' > /tmp/test_tb_data.sql

对于上述手动筛选来恢复单库或单表的方法，看起来简单方便，其实隐藏着一个小坑，下面我们来具体演示下：

# 备份整个实例mysqldump -uroot -pxxxx -R -E --single-transaction --all-databases > all_db.sql# 手动备份下test_tb 然后删除test_tbmysql> create table test_tb_bak like test_tb;Query OK, 0 rows affected (0.03 sec)mysql> insert into test_tb_bak select * from test_tb;Query OK, 4 rows affected (0.02 sec)Records: 4 Duplicates: 0 Warnings: 0mysql> drop table test_tb;Query OK, 0 rows affected (0.02 sec)# 从全备中筛选test_db建表及插数据语句cat all_db.sql | sed -e '/./{H;$!d;}' -e 'x;/CREATE TABLE `test_tb`/!d;q' > test_tb_info.sql cat all_db.sql | grep --ignore-case 'insert into `test_tb`' > test_tb_data.sql# 查看得到的语句 貌似没问题cat test_tb_info.sqlDROP TABLE IF EXISTS `test_tb`;/*!40101 SET @saved_cs_client   = @@character_set_client */;/*!40101 SET character_set_client = utf8 */;CREATE TABLE `test_tb` ( `inc_id` int(11) NOT NULL AUTO_INCREMENT COMMENT '自增主键', `col1` int(11) NOT NULL, `col2` varchar(20) DEFAULT NULL, `col_dt` datetime DEFAULT NULL, `create_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间', `update_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '修改时间', PRIMARY KEY (`inc_id`)) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 COMMENT='测试表';/*!40101 SET character_set_client = @saved_cs_client */;cat test_tb_data.sqlINSERT INTO `test_tb` VALUES (1,1001,'dsfs','2020-08-04 12:12:36','2020-09-17 06:19:27','2020-09-17 06:19:27'),(2,1002,'vfsfs','2020-09-04 12:12:36','2020-09-17 06:19:27','2020-09-17 06:19:27'),(3,1003,'adsfsf',NULL,'2020-09-17 06:19:27','2020-09-17 06:19:27'),(4,1004,'walfd','2020-09-17 14:19:27','2020-09-17 06:19:27','2020-09-18 07:52:13');# 执行恢复单表操作mysql -uroot -pxxxx testdb < test_tb_info.sqlmysql -uroot -pxxxx testdb < test_tb_data.sql# 查看恢复数据 并和备份表比对mysql> select * from test_tb;+--------+------+--------+---------------------+---------------------+---------------------+| inc_id | col1 | col2  | col_dt       | create_time     | update_time     |+--------+------+--------+---------------------+---------------------+---------------------+|   1 | 1001 | dsfs  | 2020-08-04 12:12:36 | 2020-09-17 06:19:27 | 2020-09-17 06:19:27 ||   2 | 1002 | vfsfs | 2020-09-04 12:12:36 | 2020-09-17 06:19:27 | 2020-09-17 06:19:27 ||   3 | 1003 | adsfsf | NULL        | 2020-09-17 06:19:27 | 2020-09-17 06:19:27 ||   4 | 1004 | walfd | 2020-09-17 14:19:27 | 2020-09-17 06:19:27 | 2020-09-18 07:52:13 |+--------+------+--------+---------------------+---------------------+---------------------+4 rows in set (0.00 sec)mysql> select * from test_tb_bak;+--------+------+--------+---------------------+---------------------+---------------------+| inc_id | col1 | col2  | col_dt       | create_time     | update_time     |+--------+------+--------+---------------------+---------------------+---------------------+|   1 | 1001 | dsfs  | 2020-08-04 12:12:36 | 2020-09-17 14:19:27 | 2020-09-17 14:19:27 ||   2 | 1002 | vfsfs | 2020-09-04 12:12:36 | 2020-09-17 14:19:27 | 2020-09-17 14:19:27 ||   3 | 1003 | adsfsf | NULL        | 2020-09-17 14:19:27 | 2020-09-17 14:19:27 ||   4 | 1004 | walfd | 2020-09-17 14:19:27 | 2020-09-17 14:19:27 | 2020-09-18 15:52:13 |+--------+------+--------+---------------------+---------------------+---------------------+4 rows in set (0.00 sec)

那么你会问了，为什么全部恢复不会出问题呢？问的好，我们看下备份文件就知道了。

# 备份文件开头-- MySQL dump 10.13 Distrib 5.7.23, for Linux (x86_64)---- Host: localhost  Database:-- -------------------------------------------------------- Server version    5.7.23-log/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;/*!40101 SET NAMES utf8 */;/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;/*!40103 SET TIME_ZONE='+00:00' */; 注意上面两行/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;# 备份文件结尾/*!40103 SET TIME_ZONE=@OLD_TIME_ZONE */;/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;/*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;/*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;-- Dump completed on 2020-09-18 15:56:40

看到这里，不知道你是否看懂了呢，可能有过备份恢复经验的同学好理解些。解决上述问题的方法也很简单，那就是在执行SQL文件前，更改当前会话时区为0，再次来演示下：

# 清空test_db表数据mysql> truncate table test_tb;Query OK, 0 rows affected (0.02 sec)# 文件开头增加时区声明vim test_tb_data.sqlset session TIME_ZONE='+00:00';INSERT INTO `test_tb` VALUES (1,1001,'dsfs','2020-08-04 12:12:36','2020-09-17 06:19:27','2020-09-17 06:19:27'),(2,1002,'vfsfs','2020-09-04 12:12:36','2020-09-17 06:19:27','2020-09-17 06:19:27'),(3,1003,'adsfsf',NULL,'2020-09-17 06:19:27','2020-09-17 06:19:27'),(4,1004,'walfd','2020-09-17 14:19:27','2020-09-17 06:19:27','2020-09-18 07:52:13');# 执行恢复并比对 发现数据正确mysql> select * from test_tb;+--------+------+--------+---------------------+---------------------+---------------------+| inc_id | col1 | col2  | col_dt       | create_time     | update_time     |+--------+------+--------+---------------------+---------------------+---------------------+|   1 | 1001 | dsfs  | 2020-08-04 12:12:36 | 2020-09-17 14:19:27 | 2020-09-17 14:19:27 ||   2 | 1002 | vfsfs | 2020-09-04 12:12:36 | 2020-09-17 14:19:27 | 2020-09-17 14:19:27 ||   3 | 1003 | adsfsf | NULL        | 2020-09-17 14:19:27 | 2020-09-17 14:19:27 ||   4 | 1004 | walfd | 2020-09-17 14:19:27 | 2020-09-17 14:19:27 | 2020-09-18 15:52:13 |+--------+------+--------+---------------------+---------------------+---------------------+4 rows in set (0.00 sec)mysql> select * from test_tb_bak;+--------+------+--------+---------------------+---------------------+---------------------+| inc_id | col1 | col2  | col_dt       | create_time     | update_time     |+--------+------+--------+---------------------+---------------------+---------------------+|   1 | 1001 | dsfs  | 2020-08-04 12:12:36 | 2020-09-17 14:19:27 | 2020-09-17 14:19:27 ||   2 | 1002 | vfsfs | 2020-09-04 12:12:36 | 2020-09-17 14:19:27 | 2020-09-17 14:19:27 ||   3 | 1003 | adsfsf | NULL        | 2020-09-17 14:19:27 | 2020-09-17 14:19:27 ||   4 | 1004 | walfd | 2020-09-17 14:19:27 | 2020-09-17 14:19:27 | 2020-09-18 15:52:13 |+--------+------+--------+---------------------+---------------------+---------------------+4 rows in set (0.00 sec)

我们在网络中很容易搜索出恢复单库或单表的方法，大多都有提到上述利用 sed 、grep 命令来手动筛选的方法。但大部分文章都未提及可能出现的问题，如果你的表字段有timestamp 类型，用这种方法要格外注意。无论面对哪种恢复需求，我们都要格外小心，不要造成越恢复越糟糕的情况，最好有个空实例演练下，然后再进行恢复。

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