1.performance_schema.session_variables doesn't exist
问题描述：当我想用mysqldump -uroot -p choose_stock > choose_stock.sql导出数据库时，出现下列错误：
mysqldump: Couldn't execute 'SHOW VARIABLES LIKE 'gtid\_mode'': Table 'performance_schema.session_variables' doesn't exist (1146)
问题解决：网上搜寻答案后，输入如下命令即可解决：
mysql_upgrade -u root -p --force
之后再重启服务器即可
service mysql restart (5.5.7版本命令)
