title: In SQL, can I get the average of a group of numbers, but only for those records with matching labels?
body: <p>I have two MySQL tables, one with information about items (called item), and another with customer reviews for those items (called review).</p>
  <p>Item contains the label as a text-based primary key, along with some other attributes.
  Review contains an auto-incrementing reviewID, along with the item label as a foreign key, and then a review score out of 5.</p>
  <p>For example:</p>
  <pre><code>Item
  | LABEL | INFO_1 | INFO_2 | etc|
    book    fict     2010
    book2   nonfic   1997
  ...
  
  Review
  | REVIEWID | LABEL | SCORE |
    001        book     4
    002        book     5
    003        book2    5
  </code></pre>
  <p>I want to create a view so that I can see the average review score per item. I have tried to select</p>
  <pre><code>AVG(review.score) AS avgscore 
  </code></pre>
  <p>but that returns the same average of every review in the system, without separating it by item label. Do I need to do some kind of join or add further arguments? Sorry if this is a stupid question. I'm not exactly super-fluent in MySQL.</p>
  <p>My desired result is something like the following:</p>
  <pre><code>AverageScoreView
  | LABEL | AVGSCORE |
    book      4.5
    book2      5
  </code></pre>