Sql - write something instead of NULL values

I am doing a query like this:

select name, count(*)as num from client, work where client.id = work.idc group by name;

And i am getting result of 2 columns, name and num which i see the name and the sum of how many times each one of the names used something.

I have also clients that did nothing.

What i want to do is showing them also in the new table and instead of writing their count (which is 0 because they still did nothing) i want to write in the same column num, "still did nothing".

I heard i can do it with if or case but i have no clue how.