mysql/mariadb学习过程中出现的问题与解决

mysql> insert into student values(,'周帅','男',,'CS');
ERROR  (): Duplicate entry '' for key 'PRIMARY'(duplecate为重复的意思)
primary key 主键不能插入与其相同的字段 同 unique

ERROR  (HY000): Error on rename of './test/#sql-27c_2308' to './test/student' (errno: )
更改类型编码类型时 出现此错误一般为有外键约束 解决方法 暂时停止外键检查 set foreign_key_checks=;

数据库刚安装时数据库的默认编码可能并不一定为utf8的格式,那么存入中文数据时可能会出错以下为解决方法:
.首先将mariadb的客户端以及数据库的默认编码改成utf8(基于cento7. mariadb5.):
查看mariadb/mysql数据库的相关编码:
mysql> show variables like 'character%';
+--------------------------+----------------------------+
| Variable_name            | Value                      |
+--------------------------+----------------------------+
| character_set_client     | utf8                       |
| character_set_connection | utf8                       |
| character_set_database   | latin1                     |
| character_set_filesystem | binary                     |
| character_set_results    | utf8                       |
| character_set_server     | latin1                     |
| character_set_system     | utf8                       |
| character_sets_dir       | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+
 rows in set (0.38 sec)
这其中有database和server不是utf8的格式,则进入/etc/my.cnf.d目录中更改配置文件:
在client.cnf中的[client]下添加:
[client]
default-character-set=utf8
在server.cnf中的[mysqld]下添加:
[mysqld]
character-set-server=utf8
重启数据库,查看mariadb/mysql数据库的相关编码:
mysql> show variables like 'character%';
+--------------------------+----------------------------+
| Variable_name            | Value                      |
+--------------------------+----------------------------+
| character_set_client     | utf8                       |
| character_set_connection | utf8                       |
| character_set_database   | utf8                       |
| character_set_filesystem | binary                     |
| character_set_results    | utf8                       |
| character_set_server     | utf8                       |
| character_set_system     | utf8                       |
| character_sets_dir       | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+
 rows in set (0.38 sec)
.因为已建立的数据库默认的编码格式不为utf8则虽然更改默认的编码格式后,已建立的数据库并不会更改,在之后新创建的表格中也会默认继承数据库原来的编码格式,因此这里来更改单个数据库的默认编码:
首先选择要更改的数据库
mysql> use test
Database changed
查看test数据库的编码格式:
mysql> show create database test;
+----------+-----------------------------------------------------------------+
| Database | Create Database                                                 |
+----------+-----------------------------------------------------------------+
| test     | CREATE DATABASE `test` /*!40100 DEFAULT CHARACTER SET latin1 */ |
+----------+-----------------------------------------------------------------+
 row in set (0.38 sec)
更改数据库的编码格式:
mysql> alter database test default character set utf8;
Query OK,  row affected (0.38 sec)
再次查看是否更改成功:
mysql> show create database test;
+----------+---------------------------------------------------------------+
| Database | Create Database                                               |
+----------+---------------------------------------------------------------+
| test     | CREATE DATABASE `test` /*!40100 DEFAULT CHARACTER SET utf8 */ |
+----------+---------------------------------------------------------------+
 row in set (0.38 sec)
新建一个表格来确认:
mysql> create table emp(empno numeric() primary key,ename varchar() not null,job varchar(),mgr numeric(),hiredate date, sal numeric(,),comm numeric(,),deptno numeric());
Query OK,  rows affected (0.41 sec)
查看emp表格中的相关信息:
mysql> show full columns from emp;

查看student表中的编码:
mysql> show full columns from student;

修改字段中的编码:
mysql> alter table student convert to character set utf8 collate utf8_general_ci;
ERROR 1025 (HY000): Error on rename of './test/#sql-27c_2308' to './test/student' (errno: 150)
更改类型编码类型时 出现此错误一般为有外键约束 解决方法 暂时停止外键检查 set foreign_key_checks=0;
mysql> show full columns from student;

再来查看一下,可见所有的编码都已经改成utf8的格式;
2018-04-29 13:25:12