MySQL遇到的小问题

        这篇博客，如同linux上遇到的小问题一样，一直更新，把平时项目中遇到的MySQL问题及解决方法都贴在这，以供自己以后查看。

        1、项目中有的表字段用到了枚举型（enum），如“`is_show` enum('0','1') NOT NULL COMMENT '是否显示 0否 1是'”，这时要查询表中显示的记录，一开始是这么写的，“SELECT * FROM tablename WHERE is_show = 1”，可实际得到的数据却是未显示的，仔细查看了下建表语句，发现应该要加上引号，否则会被认为是0的，“SELECT * FROM tablename WHERE is_show = "1"”。

        2、以root身份进入mysql内，没有发现mysql库，可能是权限没有了，退出去，关掉mysql进程，以“/www/mysql/bin/mysqld -uroot --skip-grant-tables”方式启动

service mysqld stop/www/mysql/bin/mysqld -uroot --skip-grant-tablesmysqluse mysql;update user set Select_priv ='Y' where user = 'root';update user set Insert_priv ='Y' where user = 'root';update user set Update_priv ='Y' where user = 'root';update user set Delete_priv ='Y' where user = 'root';update user set Create_priv ='Y' where user = 'root';update user set Drop_priv ='Y' where user = 'root';update user set Reload_priv ='Y' where user = 'root';update user set Shutdown_priv ='Y' where user = 'root';update user set Process_priv ='Y' where user = 'root';update user set File_priv ='Y' where user = 'root';update user set Grant_priv ='Y' where user = 'root';update user set References_priv ='Y' where user = 'root';update user set Index_priv ='Y' where user = 'root';update user set Alter_priv ='Y' where user = 'root';update user set Show_db_priv ='Y' where user = 'root';update user set Super_priv ='Y' where user = 'root';update user set Create_tmp_table_priv ='Y' where user = 'root';update user set Lock_tables_priv ='Y' where user = 'root';update user set Execute_priv ='Y' where user = 'root';update user set Repl_slave_priv ='Y' where user = 'root';update user set Repl_client_priv ='Y' where user = 'root';update user set Create_view_priv ='Y' where user = 'root';update user set Show_view_priv ='Y' where user = 'root';update user set Create_routine_priv ='Y' where user = 'root';update user set Alter_routine_priv ='Y' where user = 'root';update user set Create_user_priv ='Y' where user = 'root';update user set Event_priv ='Y' where user = 'root';update user set Trigger_priv ='Y' where user = 'root';update user set Create_tablespace_priv ='Y' where user = 'root';flush privileges;exit;#停止刚刚那个mysqld进程，再重启mysqlps aux | grep mysqldkill 进程service mysqld start

        3、重装mysql前，一定得备份下数据表，mysiam引擎的好说，innodb的除了备份库名字的目录外，还的备份ibdata文件，因为innodb引擎表的数据和索引存在ibdata内。

        4、导入sql文件时，报“Got a packet bigger than 'max_allowed_packet' bytes”，在my.cnf中的[MySQLd]下面加上max_allowed_packet=10M，这个值大于导入的文件即可，重启MySQL。

        5、接着第四条，进入MySQL，use sugarcrm，之后提示“Reading table information for completion of table and column namesYou can turn off this feature to get a quicker startup with -A”，因为导入的数据很大，有2G多，这个库也很大，表也很多。在use 该库时，MySQL需要预读数据库信息，由于量大，于是出现提示，只需要在进入MySQL时，加上个-A参数即可，“mysql -uroot -ppassword -A”。

        6、如果本地或是服务器导入sql文件时，经常这两种错误，‘Lost connection to MySQL server during query’、‘Got a packet bigger than 'max_allowed_packet' bytes’，那么需要在配置文件中重新设置max_allowed_packet。

        7、select  ... into  outfile ...方式导出数据，只能在连接的MySQL服务器上导出，没有加路径，则为/var/lib/mysql/当前数据库文件目录，加了目录则在/tmp目录里，若是在其他服务器远程连接，则会报“ERROR 1 (HY000) at line 1: Can't create/write to file ”错误。

        8、MySQL 5.6 去掉严格模式

vim /etc/my.cnfsql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES sql_mode=NO_ENGINE_SUBSTITUTION

        9、启动MySQL时报“Starting MySQL.. ERROR! The server quit without updating PID file (/www/mysql/data/FJR-bt-kvm-72-26.pid)”

/www/mysql/data/FJR-bt-kvm-72-26.pid没有权限chmod 777 /www/mysql/data/FJR-bt-kvm-72-26.pid#如果解决不了，可以移步看看这个 http://blog.rekfan.com/articles/186.html

        10、进入mysql库后，grant 操作报“ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)”

update user set Create_tablespace_priv ='Y' where user = 'root';flush privileges;

        11、删除原有主键，重新设置主键

1、取消主键alter table `table_name` drop primary key;2、添加a_idalter table `table_name` add column `a_id` int(11) unsigned not null first; 3、添加主键ALTER  TABLE  `table_name` MODIFY COLUMN  `a_id` INT(11) NOT NULL AUTO_INCREMENT, add PRIMARY KEY (`a_id`);