use email as username

Hi,

I am a regular user of moodle

my moodle version is 2.3

"I want that instead of entering username in moodle, user enter theire email, and this email id used as username. but as we all know that we have another email field(I know that in username field we can enter the email but how to make this email as user email at back end

for example: I want these fields

email: (will act as a username)

email again:

password:

I dont want username fields

Is there any code or mysql query which enter email in the username field

)"

can any1 help me sort out this problem in moodle. I want to know where mysql queries reside in moodle.

any help?