title: sql where has two conditions but one field has index, can it improve performence?
body: <p>I have a sql statement:</p>
  
  <pre><code>SELECT * FROM table 
  WHERE field1 = value1 AND field2 = value2
  </code></pre>
  
  <p>If I create a index for column field1 and field2 does not have index. Can this improve the performance. IF so why ?</p>