Do not display null lines in mysql results

I have a simple mysql query

SELECT usr_contact FROM $usr_

I use PDO to connect this table has rows that have empty fields so

-----------------------
|   id    |usr_contact|
-----------------------
|  1234   |    null   |
-----------------------
|  null   |   147852  |

In the query it creates

contact
---
X
---
147852

How do I not display the empty fields in the result?