thank you all for your answers.
It's safe to have multiple statements running in a while, or there is the risk of confusion (I mean having some result sent indeed another one)? I mean: 
my $sth1 = $dbh->prepare( $sql1 ); # it can be a select
my $sth2 = $dbh->prepare( $sql2 ); # it can be an insert


while(my $var=@arr){
$sth1->execute($param1);
$sth2->execute($param2);
}

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In reply to Re^3: prepared statement by saintex
in thread prepared statement by saintex

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