merge合并表的要求
1.合并的表使用的必须是MyISAM引擎
2.表的结构必须一致，包括索引、字段类型、引擎和字符集
实例：
create table if not exists user1(
id int(11) not null auto_increment,
name varchar(50) default null,
sex int(1) not null default 0,
primary key (id)
)engine = MyISAM default charset = utf8 auto_increment=1;
create table if not exists user2(
id int(11) not null auto_increment,
name varchar(50) default null,
sex int(1) not null default 0,
primary key (id)
)engine = MyISAM default charset = utf8 auto_increment=1;
create table if not exists alluser(
id int(11) not null auto_increment,
name varchar(50) default null,
sex int(1) not null default 0,
primary key (id)
)engine = merge union=(user1,user2) insert_method = last auto_increment=1;
执行insert into alluser (name,sex) values ('tian',1);报错如下：
ERROR 1168 (HY000): Unable to open underlying table which is differently defined or of non-MyISAM type or doesn't exist
百度了一下原来是默认字符集没写，修改如下
create table if not exists alluser1(
id int(11) not null auto_increment,
name varchar(50) default null,
sex int(1) not null default 0,
primary key (id)
)engine = merge union=(user1,user2) insert_method = last auto_increment=1 default charset=utf8;
执行insert into alluser1 (name,sex) values ('tian',1);成功
执行select * from alluser1;显示如下：
+----+------+-----+
| id | name | sex |
+----+------+-----+
| 1 | tian | 1 |
+----+------+-----+
执行select * from user2;显示如下：
+----+------+-----+
| id | name | sex |
+----+------+-----+
| 1 | tian | 1 |
+----+------+-----+
