mysql> SELECT * FROM wp_options WHERE option_name='template' or option_name='stylesheet';
+-----------+-------------+---------------+----------+
| option_id | option_name | option_value | autoload |
+-----------+-------------+---------------+----------+
| 41 | template | mytheme | yes |
| 42 | stylesheet | mytheme | yes |
+-----------+-------------+---------------+----------+
2 row in set (0.00 sec)
mysql> SELECT option_name,option_value FROM wp_options WHERE wp_value like '%mytheme%';
mysql> BEGIN;
mysql> UPDATE wp_options SET option_VALUE="twentyfifteen" WHERE option_name='stylesheet';
Query OK, 1 row affected (0.05 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> UPDATE wp_options SET option_VALUE="twentyfifteen" WHERE option_name='template';
Query OK, 1 row affected (0.05 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> SELECT * FROM wp_options WHERE option_name='template' or option_name='stylesheet';
+-----------+-------------+---------------+----------+
| option_id | option_name | option_value | autoload |
+-----------+-------------+---------------+----------+
| 41 | template | twentyfifteen | yes |
| 42 | stylesheet | twentyfifteen | yes |
+-----------+-------------+---------------+----------+
2 row in set (0.00 sec)
mysql> COMMIT;