MariaDB [test]> show create table test2\G

*************************** 1. row ***************************

       Table: test2

Create Table: CREATE TABLE `test2` (

  `num` int(11) NOT NULL,

  `name` varchar(255) DEFAULT NULL

) ENGINE=CONNECT DEFAULT CHARSET=latin1 `table_type`=CSV `file_name`='/t/qq1' `sep_char`=';'

1 row in set (0.01 sec)

MariaDB [test]> \! cat /t/qq1

fdag afdg dfgMariaDB [test]> 

MariaDB [test]> alter table test2 add index(num);

ERROR 2013 (HY000): Lost connection to MySQL server during query

MariaDB [test]> 

Thread 1 (Thread 0x7ffa6fbdeb00 (LWP 23991)):

#0  __longjmp () at ../sysdeps/x86_64/__longjmp.S:67

#1  0x24414d072e092f80 in ?? ()

Backtrace stopped: Cannot access memory at address 0x24414d072e092f80