修改MySQL表varchar字段的小实验

将actor表的first_name的varchar(45) ，修改为varchar(60)

[root@vhost1 ~]# mysql -uroot -p -S /mysqldata/tmp/mysql33061.sock
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mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sakila |
| test |
+--------------------+
5 rows in set (0.00 sec)

mysql> use sakila;

mysql> show create table actor\G;
*************************** 1. row ***************************
Table: actor
Create Table: CREATE TABLE `actor` (
`actor_id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
`first_name` varchar(45) NOT NULL,
`last_name` varchar(45) NOT NULL,
`last_update` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`actor_id`),
KEY `idx_actor_last_name` (`last_name`)
) ENGINE=InnoDB AUTO_INCREMENT=201 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

创建中间表actor_tmp

mysql> create table actor_tmp(
-> `actor_id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
-> `first_name` varchar(60) not null,
-> `last_name` varchar(45) NOT NULL,
-> `last_update` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
-> PRIMARY KEY (`actor_id`),
-> KEY `idx_actor_last_name` (`last_name`)
-> ) ENGINE=InnoDB AUTO_INCREMENT=201 DEFAULT CHARSET=utf8;
Query OK, 0 rows affected (0.08 sec)

mysql>lock table actor read; 

mysql> system cp /mysqldata/33061/sakila/actor_tmp.frm /mysqldata/33061/sakila/actor.frm
mysql> flush tables;

mysql> show create table actor\G;
*************************** 1. row ***************************
Table: actor
Create Table: CREATE TABLE `actor` (
`actor_id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
`first_name` varchar(60) NOT NULL,
`last_name` varchar(45) NOT NULL,
`last_update` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`actor_id`),
KEY `idx_actor_last_name` (`last_name`)
) ENGINE=InnoDB AUTO_INCREMENT=201 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

ERROR:
No query specified

mysql> select count(*) from actor;
+----------+
| count(*) |
+----------+
| 200 |
+----------+
1 row in set (0.00 sec)

mysql> unlock tables;
Query OK, 0 rows affected (0.00 sec)