Here is a PHP solution ready for use with a n:m (many-to-many relationship) table :
// get data
$table_1 = get_table_1_rows();
$table_2_fk_id = 123;
// prepare first part of the query (before values)
$query = "INSERT INTO `table` (
`table_1_fk_id`,
`table_2_fk_id`,
`insert_date`
) VALUES ";
//loop the table 1 to get all foreign keys and put it in array
foreach($table_1 as $row) {
$query_values[] = "(".$row["table_1_pk_id"].", $table_2_fk_id, NOW())";
}
// Implode the query values array with a coma and execute the query.
$db->query($query . implode(',',$query_values));