MySQL parse Column to obtain a numerical section and add them up

I have the following table:

+------------------+
|   ColumnName     |
+------------------+
| 1 Slap  开发者_StackOverflow中文版         |
+------------------+
| 13 Slap          |
+------------------+
| 2 Slap           |
+------------------+

With only MySQL how can I parse that ColumnName to only grab the numerical value and add them all up?

The output of the query should be 16 if doing it on the above table.

---

SELECT SUM(CAST(ColumnName as SIGNED)) FROM TableName

(or UNSIGNED if you don't have any negative numbers)

Edit: Test data to satisfy the skeptics.

mysql> select * from testtable;
+---------+
| testcol |
+---------+
| 1 Slap  |
| 13 Slap |
| 2 Slap  |
+---------+
3 rows in set (0.00 sec)

mysql> select sum(cast(testcol as unsigned)) from testtable;
+--------------------------------+
| sum(cast(testcol as unsigned)) |
+--------------------------------+
|                             16 |
+--------------------------------+
1 row in set, 3 warnings (0.00 sec)

mysql>

---

SELECT SUM(CAST(LEFT(ColumnName, INSTR(ColumnName, ' ')) as SIGNED))
FROM Table