The easiest way to achieve merging two MySQL databases is to essentially copy data from a table to another table and back again.

Both databases need to exist on the same account. If they do not, you will need to create a backup of one and move it over to the same account as your second database. If both databases have the same name, you will need to also rename one before moving.

Once both are on the same account, log in to either SSH or cPanel...

cPanel

1. From cPanel, click the phpMyAdmin icon

2. Click the SQL tab at the top
   
   You will see where it says, 'Run SQL query/queries on server "localhost":'

3. In the text box below that, insert the following code, but replace DB1 and DB2 with the database names and replace TABLE1 with the table name you are trying to merge:

   INSERT INTO DB1.TABLE1 SELECT * FROM DB2.TABLE1
   
   

4. Click the Go button

5. Repeat for any other tables you want to merge

Shell (SSH)

1. From SSH, type the command to access MySQL
   
   Here is the format, but replace MYNAME with your username and PASS with your password:

   ​mysql -u MYNAME -pPASS
   

2. Now type the following code, but replace DB1 and DB2 with the database names and replace TABLE1 with the table name you are trying to merge:

   INSERT INTO DB1.TABLE1 SELECT * FROM DB2.TABLE1;

3. Press the Enter key

4. Repeat for any other tables you want to merge

Here is what mine looks like:

Tip! Use REPLACE INTO instead of INSERT INTO to have the data from DB2 overwrite the data in DB1 if they share a primary/unique key.