if this week is empty, don't show this week

My program get weeks in weeks table. And I have challange table and challange_week column in challange table for 开发者_StackOverflowunite two table.

I want to if gotten week is empty, don't show this week. Can i do this with just one SQL query?

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left outer join?

    select * from weeks w
    left outer join challange c on w.week = c.challange_week
    where c.challange_week is not null