如下错误情况：
mysql> SELECT * FROM my_table WHERE name = 'Smith AND age < 30;
'>
因为 mysql 引擎在等待单引号"'"结束，因此以下命令全部无效：
\q
quit;
exit;
ctrl+c
必须用如下方法，补上结束符的单引号“'”并执行清屏命令“\c”即可：
mysql> SELECT * FROM my_table WHERE name = 'Smith AND age < 30;
'> '\c
mysql>
其它符号以此类推：
Prompt Meaning
mysql> Ready for new query
-> Waiting for next line of multiple-line query
'> Waiting for next line, waiting for completion of a string that began with a single quote (')
"> Waiting for next line, waiting for completion of a string that began with a double quote (")
`> Waiting for next line, waiting for completion of an identifier that began with a backtick (`)
/*> Waiting for next line, waiting for completion of a comment that began with /*
更详细请查阅官方文档: https://dev.mysql.com/doc/refman/8.0/en/entering-queries.html