====== NULL Values ======
===== searching for =====
If you want to search for column values that are NULL, you cannot use an expr = NULL test. The following statement returns no rows, because expr = NULL is never true for any expression:
<code mysql>
mysql> SELECT * FROM my_table WHERE phone = NULL;
</code>

To look for NULL values, you must use the IS NULL test. The following statements show how to find the NULL phone number and the empty phone number:
<code mysql>
mysql> SELECT * FROM my_table WHERE phone IS NULL;
mysql> SELECT * FROM my_table WHERE phone = '';
</code>