Why do you want to close the connection anyway?

There should be no problem with something like:

sth1 = prepare select
sth1->execute
sth2 = prepare select
sth2->execute

sth3 = prepare insert

while () {
  sth1->fetch
  sth2->fetch

  sth3->execute
}

sth1->finish
sth2->finish
sth3->finish
[download]

Unless your database prevents having multiple statements at the same time.