<?php
global $wpdb;
?>

<?php
$results = $wpdb->get_results("select * from $wpdb->posts where post_status = 'draft' and post_author = 5");
foreach ($results as $result) {
	echo $result->post_title;
}
?>

<?php
$row = $wpdb->get_row("select * from $wpdb->links where link_id = 25");
echo $row->link_id; // prints "25"
?>

<?php
$wpdb->insert(
	$wpdb->posts,
	array(
		'column1' => 'value1', // string
		'column2' => 123, // decimal
		'column3' => 12.5 // float
	),
	array( '%s', '%d', '%f' ) // format (optional) (string type by default)
);
$insert_id = $wpdb->insert_id; // the value of AUTO_INCREMENT column after insert
?>

<?php
$wpdb->update(
	$wpdb->posts,
	array(
		'column1' => 'value1', // string
		'column2' => 22 // decimal
	),
	array( 'ID' => 15 ), // where
	array( '%s', '%d' ), // format (optional)
	array( '%d' ) // where_format (optional)
);
?>

<?php
$wpdb->query( $wpdb->prepare(
"delete from tablename where post_id=%d and meta_key=%s", $number, $string
));
?>