How do I ensure I caught all errors from MySQLi::multi_query?

The docs for multi_query say:

Returns FALSE if the first statement failed. To retrieve subsequent errors from other statements you have to call mysqli_next_result() first.

The docs for next_result say:

Returns TRUE on success or FALSE on failure.

Finally, the example posted in the docs for multi_query use the return value from next_result to determine when there are no more queries; e.g. to stop looping:

<?php
$mysqli = new mysqli("localhost", "my_user", "my_password", "world");

/* check connection */
if (mysqli_connect_errno()) {
    printf("Connect failed: %sn", mysqli_connect_error());
    exit();
}

$query  = "SELECT CURRENT_USER();";
$query .= "SELECT Name FROM City ORDER BY ID LIMIT 20, 5";

    /* execute multi query */
    if ($mysqli->multi_query($query)) {
        do {
            /* store first result set */
            if ($result = $mysqli->store_result()) {
                while ($row = $result->fetch_row()) {
                    printf("%sn", $row[0]);
                }
                $result->free();
            }
            /* print divider */
            if ($mysqli->more_results()) {
                printf("-----------------n");
            }
        } while ($mysqli->next_result()); // <-- HERE!
    }

    /* close connection */
    $mysqli->close();
    ?>

I don’t know the number of queries provided, nor do I know anything about the SQL that I’m going to execute. I therefore can’t just compare the number of queries against the number of returned results. Yet I want to display an error message to the user if, say, the third query was the broken query. But I don’t seem to have a way to tell if next_result failed because there were no more queries to execute, or if it’s because there was an error in the SQL syntax.

How can I check all the queries for errors?

Answer

Despite the code example in the docs, perhaps the better method would be something like this:

if ($mysqli->multi_query(...)) {
  do {
    // fetch results

    if (!$mysqli->more_results()) {
      break;
    }
    if (!$mysqli->next_result()) {
      // report error
      break;
    }
  } while (true);
}