Does seeded rand() with unique integer return unique number?

There is id auto-increment primary key column and serial int column in a table. How to insert a 7 digit unique random number into serial?

Can we say that seeded rand() with unique id returns unique value?

FLOOR(1111111 + (RAND( <uniqe id> ) * 8888888))

Can it done with php mt_srand and mt_rand?