title: What is the difference between this 3 query
body: <p>Is there any difference between this 3 query?</p>
  
  <p>query 1</p>
  
  <pre><code>$query = "INSERT INTO reserve( c_id, c_username, r_id, r_name, checkin, checkout)";
  $query .= " VALUES ( $c_id, $c_username, $r_id, $r_name, $checkin, $checkout )";
  </code></pre>
  
  <p>query 2</p>
  
  <pre><code>$sql = "INSERT INTO reserve( c_id, c_username, r_id, r_name, checkin, checkout)
  VALUES ( '$c_id' , '$c_username', '$r_id', '$r_name', '$checkin', '$checkout' )";
  </code></pre>
  
  <p>query 3</p>
  
  <pre><code>$result = $mysqli-&gt;query("INSERT INTO reserve (c_id, c_username, r_id, r_name, checkin, checkout) VALUES ('$c_id' , '$c_username', '$r_id', '$r_name', '$checkin', '$checkout');")
  </code></pre>
  
  <p>And which one should I use to select a data from my database and which one should I use to insert data into database</p>