I'm using MySQL 5.5.37. I want to eliminate the warnings from my update statement, which are shown below ...

update resource r 
    set grade_id = convert(substring_index(substring_index(
                   r.description, 'Grade ', -1), ' ', 1), unsigned integer) 
    where r.description like '% Grade%' 
      and CONVERT(SUBSTRING_INDEX(SUBSTRING_INDEX(
                   r.description, 'Grade ', -1), ' ' ,1),UNSIGNED) > 0;

Query OK, 0 rows affected, 7 warnings (0.02 sec)
Rows matched: 1333  Changed: 0  Warnings: 7

mysql> show warnings;
+---------+------+--------------------------------------------------+
| Level   | Code | Message                                          |
+---------+------+--------------------------------------------------+
| Warning | 1292 | Truncated incorrect INTEGER value: ''            |
| Warning | 1292 | Truncated incorrect INTEGER value: ''            |
| Warning | 1292 | Truncated incorrect INTEGER value: ''            |
| Warning | 1292 | Truncated incorrect INTEGER value: 'MyCo'        |
| Warning | 1292 | Truncated incorrect INTEGER value: 'MyCo'        |
| Warning | 1292 | Truncated incorrect INTEGER value: 'MyCo'        |
| Warning | 1292 | Truncated incorrect INTEGER value: 'MyCo'        |
+---------+------+--------------------------------------------------+

What I do not understand is how I can rewrite my query differently given that none of the values being updated match what the warnings are complaining about. BElow is my query where I list the distinct values that are being updated ...

mysql> select distinct substring_index(substring_index(
              r.description, 'Grade ', -1), ' ', 1)
          from resource r
          where r.description like '% Grade%'
            and CONVERT(SUBSTRING_INDEX(SUBSTRING_INDEX(
              r.description, 'Grade ',-1),' ',1),UNSIGNED) > 0;
+-----------------------------------------------------------------------+
| substring_index(substring_index(r.description, 'Grade ', -1), ' ', 1) |
+-----------------------------------------------------------------------+
| 7                                                                     |
| 8                                                                     |
| 11                                                                    |
| 9                                                                     |
| 12                                                                    |
| 10                                                                    |
| 6                                                                     |
+-----------------------------------------------------------------------+

How do I rewrite my update statement so that it updates the same values without tryihng to truncate incorrect integers?