MySQL backfill missing data where records have one common field
kim,,,55555,kim@domain.com
kim,Longmont,CO,55555,kim@domain.com
kim,,,,kim@domain.com

kim,Longmont,CO,55555,kim@domain.com
kim,Longmont,CO,55555,kim@domain.com
kim,Longmont,CO,55555,kim@domain.com

update t2,t1 set t2.first_name=
case when t2.first_name=''
then t1.first_name
else t2.first_name end
where t2.actor_id=t1.actor_id
and t1.first_name!='';

mysql> select * from t2 limit 10;
+----------+------------+--------------+---------------------+
| actor_id | first_name | last_name    | last_update         |
+----------+------------+--------------+---------------------+
|        1 |            | GUINESS      | 2012-06-29 08:36:22 |
|        2 |            | WAHLBERG     | 2012-06-29 08:36:22 |
|        3 |            | CHASE        | 2012-06-29 08:36:22 |
|        4 |            | DAVIS        | 2012-06-29 08:36:22 |
|        5 |            | LOLLOBRIGIDA | 2012-06-29 08:36:22 |
|        6 |            | NICHOLSON    | 2012-06-29 08:36:22 |
|        7 |            | MOSTEL       | 2012-06-29 08:36:22 |
|        8 |            | JOHANSSON    | 2012-06-29 08:36:22 |
|        9 |            | SWANK        | 2012-06-29 08:36:22 |
|       10 | CHRISTIAN  | GABLE        | 2006-02-15 04:34:33 |
+----------+------------+--------------+---------------------+
10 rows in set (0.00 sec)

mysql> select * from t1 order by actor_id limit 10;
+----------+------------+--------------+---------------------+
| actor_id | first_name | last_name    | last_update         |
+----------+------------+--------------+---------------------+
|        1 | PENELOPE   | GUINESS      | 2006-02-15 04:34:33 |
|        1 | a          |              | 0000-00-00 00:00:00 |
|        2 | NICK       | WAHLBERG     | 2006-02-15 04:34:33 |
|        3 | ED         | CHASE        | 2006-02-15 04:34:33 |
|        4 | JENNIFER   | DAVIS        | 2006-02-15 04:34:33 |
|        5 | JOHNNY     | LOLLOBRIGIDA | 2006-02-15 04:34:33 |
|        6 | BETTE      | NICHOLSON    | 2006-02-15 04:34:33 |
|        7 | GRACE      | MOSTEL       | 2006-02-15 04:34:33 |
|        8 | MATTHEW    | JOHANSSON    | 2006-02-15 04:34:33 |
|        9 | JOE        | SWANK        | 2006-02-15 04:34:33 |
+----------+------------+--------------+---------------------+
10 rows in set (0.00 sec)

mysql> update t2,t1 set t2.first_name=case when t2.first_name='' then t1.first_name else t2.first_name end where t2.actor_id=t1.actor_id and t1.first_name!='';
Query OK, 9 rows affected (0.03 sec)
Rows matched: 200  Changed: 9  Warnings: 0

mysql> select * from t2 limit 10;
+----------+------------+--------------+---------------------+
| actor_id | first_name | last_name    | last_update         |
+----------+------------+--------------+---------------------+
|        1 | PENELOPE   | GUINESS      | 2012-06-29 08:37:34 |
|        2 | NICK       | WAHLBERG     | 2012-06-29 08:37:34 |
|        3 | ED         | CHASE        | 2012-06-29 08:37:34 |
|        4 | JENNIFER   | DAVIS        | 2012-06-29 08:37:34 |
|        5 | JOHNNY     | LOLLOBRIGIDA | 2012-06-29 08:37:34 |
|        6 | BETTE      | NICHOLSON    | 2012-06-29 08:37:34 |
|        7 | GRACE      | MOSTEL       | 2012-06-29 08:37:34 |
|        8 | MATTHEW    | JOHANSSON    | 2012-06-29 08:37:34 |
|        9 | JOE        | SWANK        | 2012-06-29 08:37:34 |
|       10 | CHRISTIAN  | GABLE        | 2006-02-15 04:34:33 |
+----------+------------+--------------+---------------------+
10 rows in set (0.00 sec)