第二个参数是手动设置唯一索引的名称.将数组用作第一个参数，以在多个列之间创建唯一键.

The second param is to manually set the name of the unique index. Use an array as the first param to create a unique key across multiple columns.

$table->unique(array('mytext', 'user_id'));

或(稍微整洁)

$table->unique(['mytext', 'user_id']);