Can't store a record of the date/time of suceessful logins in a second database

[phpstudent71]

I have written a login application where the user can register or login on the same page.  The registration goes to a database called customer.  The login section checks to see if the login is valid (using customer database).  Now I need to store the date/time of successful logins in another database called UserLogin.  I am having trouble joining the 2 database and can't get the code right to get the date/time of user logins to store in the database.  I have been trying to figure this out forever.  Could someone please help before I loose my mind!  Thanks.