mysql> source dba_current_database.sql
+------------+
| database() |
+------------+
| NULL       |
+------------+
1 row in set (0.00 sec)


mysql> use test;
Database changed


mysql> source dba_current_database.sql
+------------+
| database() |
+------------+
| test       |
+------------+
1 row in set (0.00 sec)