SELECT rec_num, GROUP_CONCAT(location)
FROM tbl
GROUP BY rec_num;
Example:
mysql> SELECT state, GROUP_CONCAT(city) AS 'big cities'
-> FROM us
-> WHERE population > 600000
-> GROUP BY state;
+-------+----------------------------------------------+
| state | big cities |
+-------+----------------------------------------------+
| AZ | Phoenix |
| CA | Los Angeles,San Diego,San Francisco,San Jose |
| FL | Jacksonville |
| IL | Chicago |
| IN | Indianapolis |
| MD | Baltimore |
| MI | Detroit |
| NY | New York |
| OH | Columbus |
| PA | Philadelphia |
| TN | Memphis |
| TX | Austin,Dallas,Fort Worth,Houston,San Antonio |
+-------+----------------------------------------------+
(JOIN and LEFT JOIN are not critical to this answer, since the one-to-many relationship is embodied in a single table.)