My comment is about having multiple rows, and only desiring one of those multiple rows per group. Joins are for when you want one to many. Applies are for when you have one to many, but want to filter out all except a one to one. Scenario: For 100 members, give me each their best phone number (where each could have several numbers). More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.