inserting + sorting

[Mateus Almeida da Silva]

Hello,
I'm experimenting some things in MySQL, and having some trouble with a special task, which is this:

-> 1st part:
There is a table "sell_registry", which has two important columns:
a. the first column, "client_code", has a special unique code assigned to each costumer;
b. the second columns, "sell_date", has the date in which the client bought a car.

Ok, so I need to transfer the column "sell_date" to another table, let's call it "testing". The problem is: this second table already has a "client_code" field. So, when I transfer the "sell_date" from the first to the second, I need that the data matches, according to "client_code" field.

In another words: if I have a "Phill" that bought a car in 2001-01-01, I need this date inserted in every field associated to Phill in the second table. Am I clear? How can I do that?


-> second part:
I need to do a calculus with two dates. I need to subtract: "actual date" - "sell_date" (both are "datetime" values). Problem: the result needs be in "months", in an integer value. What should I do?