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sub table_exists {
    my $db = shift;
...
    print "table not found!\n";
    $dbh->do( $create_query );
}

    my $create_query = qq{
        create table employees (
...
    my $fieldlist = join ", ", @fields;
    my $field_placeholders = join ", ", map {'?'} @fields;

    my $insert_query = qq{
        INSERT INTO employees ( $fieldlist )
...
    my $sth= $dbh->prepare( $insert_query );
# $insert_query = "INSERT INTO employees ( id, name, salary )
#            VALUES ( ?, ?, ? )";

    my ($id,  $name, $salary)  = (5, 'Sal', 4500);
    $sth->execute($id, $name, $salary);

    while ( get_values($id, $name, $salary) {
        $sth->execute($id, $name, $salary);
    }

    my @employees_lol = (
        [1, 'Fred',   5000],
...
    for (@employees_lol) {
        $sth->execute(@$_);
    }

    my @employees_loh = (
        {id => 3, name => 'Kim',  salary =>  5600},
...
    for (@employees_loh) {
        $sth->execute($_->{id}, $_->{name}, $_->{salary});
    }

    for (@employees_loh) {
        $sth->execute(@{$_}{@fields})
    }

    my $query1 = qq{select name from employees};
    my $sth= $dbh->prepare($query1);
...
    while (my ($name) = $sth->fetchrow_array) {
        push @names, $name;
    }

    my $query2 = qq{select id, name, salary from employees};
    my @names = map {$_->[1]}
        @{$dbh->selectall_arrayref($query2)};
__END__
@names = (qw(Fred Joshua Kim Dave Sal));

    #
    # either
...
__END__
$names_ref = ['Fred', 'Joshua', 'Kim', 'Dave', 'Sal'];
@names = ('Fred', 'Joshua', 'Kim', 'Dave', 'Sal');

    my $sth = $dbh->prepare($query2);
    $sth->execute();
...
        @{$sth->fetchall_arrayref([0,-2])};
__END__
@names = (qw(Fred Joshua Kim Dave Sal));

    #
    # either
...
  [ '4', 'Dave', '6000' ],
  [ '5', 'Sal', '4500' ]
];

    my $sth = $dbh->prepare($query2);
    $sth->execute();
...
  { 'salary' => '6000', 'id' => '4', 'name' => 'Dave' },
  { 'salary' => '4500', 'id' => '5', 'name' => 'Sal' }
];

    my $employees_loh = $dbh->selectall_arrayref($query2, {Slice => {}
+});

    my $sth = $dbh->prepare($query2);
    $sth->execute();
...

  { 'salary' => '4500', 'name' => 'Sal' }
];

    my %employees_h =
        map { $_->[1], $_->[2]}
...
    'Dave' => '6000' ,
    'Sal' => '4500'
    );

    #
    # either
...
  '4' => [ 'Dave', '6000' ],
  '5' => [ 'Sal', '4500' ]
);

    my $employees_hoh = $dbh->selectall_hashref($query2, 1);
__END__
...
 '4' => { 'salary' => '6000', 'id' => '4', 'name' => 'Dave' },
 '5' => { 'salary' => '4500', 'id' => '5', 'name' => 'Sal' }
};

    my $employees_hoh2 = $dbh->selectall_hashref($query2, 3);
__END__
...
  '4500' => { 'salary' => '4500', 'id' => '5', 'name' => 'Sal' },
  '6000' => { 'salary' => '6000', 'id' => '4', 'name' => 'Dave' }
 };

    my ($id, $name, $salary) ;

...
3       Kim         5600
4       Dave    6000
5       Sal         4500

    $sth->execute;

...
    $sth->bind_columns ( \( $id, $name, $salary ) );

    print "$id\t$name\t$salary\n" while $sth->fetchrow_arrayref;

    my @empl = (undef, undef, undef);
    $sth->execute;
...
    $sth->bind_columns ( \( @empl ) );    

    print join( "\t", @empl), $/ while $sth->fetchrow_arrayref;

    @empl = ( \$id, \$name, \$salary );
    $sth->execute;

    $sth->bind_columns( @empl );
    print "$id\t$name\t$salary\n" while $sth->fetch;

    my %rec = (
        emp_id => undef,
...
          "$rec{first_name}\t",
          "$rec{monthly_payment}\n"
                while $sth->fetchrow_arrayref;

    my @fields = (qw(emp_id first_name monthly_payment));

...
          "$rec{first_name}\t",
          "$rec{monthly_payment}\n"
        while $sth->fetchrow_arrayref;

    use Benchmark (qw(cmpthese));
...
fr_hashref  3858/s        --           -56%        -59%
man_hashref 8681/s      125%             --         -8%
fr_arrayref 9416/s      144%             8%          --

    $sth = $dbh->prepare(qq{
        SELECT
...
    # using a arrayref
    # columns => id,id
    # 1 1