[PDOException] SQLSTATE[HY000]: General error: 2006 MySQL server has gone away

可能是 查詢 SQL 太長，或是連線逾時

1.修改 MySQL 設定檔
/etc/my.cnf
/etc/my.cnf.d/server.cnf

[mysqld]
max_allowed_packet=16M

2.連線時加入
SET SESSION wait_timeout=65535