title: PHP-Mysql WHERE is empty AND returns results
body: <p>I am not well versed in MYSQL, and I need some guidance here. I have read multiple MYSQL WHERE statement explanations, but have not found this exact issue. I have a table called studies that has fields like id, name, author, category, format and a few others.</p>
  
  <p>I am building a filter with checkboxes to narrow down the query. I want to get all studies with a specific author AND category AND format. My problem comes when I build the query. If only the format is selected, the query returns empty because no author was selected. How do I get the results from the AND statements without the WHERE statement? Here is what I have so far...</p>
  
  <pre><code>"SELECT * FROM estudos WHERE subcategory='$subcategory' AND author='$author' AND format='$format'"
  </code></pre>