MySQL "default" result

I have a MySQL table like

id    |  text   |  category   |   active
 

I select a random line with

SELECT id, text 
 FROM table
 WHERE category = [category id] AND active = 1 
 ORDER BY RAND()
 LIMIT 1
 

Some times this would return no results (e.g. if there is no active row in a specific category). What I need to do in that case is to return a "default" row.

My question is: what is the most efficient way to do this? Should I just create an identical table but just with the default rows, which I would query if the above query gives no results? Or should I add the default rows in the same table? And how would you query it?

Note that I am excluding the possibility of generating the default text in PHP, as I want it to be customizable, without having to go and change the code.

Any suggestion is welcome!

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