When I try to create a database which already exists,
CREATE DATABASE IF NOT EXISTS test;
Query OK, 1 row affected (0.00 sec)
CREATE DATABASE IF NOT EXISTS test;
Query OK, 1 row affected, 1 warning (0.00 sec)
Why does it show 1 row affected message second time , even though it is not creating a new database with the same name?
Although the CREATE DATABASE IF NOT EXISTS test; command won't directly modify rows in an exiting instance of the test database, it will affect the actual details stored internally in the mysql database, or possibly in one of the derived meta views, like the information_schema or performance_schema etc.
The reported Query OK, 1 row affected (0.00 sec) is referring to a row in one of these internal data constructs. When you reissue the CREATE DATABASE command, and it fails gracefully thanks to the IF NOT EXISTS clause, it is still likely to store meta-data internally, maybe an accumulating field that counts warnings or similar, or even just a 'last acted on' timestamp against this database's row. In any case the stored data in this record is changed, and is reflected as an 'affected' row.
