WATCH OUT: if you mix $mysqli->multi_query and $mysqli->query, the latter(s) won't be executed!

<?php
// BAD CODE:
$mysqli->multi_query(" Many SQL queries ; "); // OK
$mysqli->query(" SQL statement #1 ; ") // not executed!
$mysqli->query(" SQL statement #2 ; ") // not executed!
$mysqli->query(" SQL statement #3 ; ") // not executed!
$mysqli->query(" SQL statement #4 ; ") // not executed!
?>

The only way to do this correctly is:

<?php
// WORKING CODE:
$mysqli->multi_query(" Many SQL queries ; "); // OK
while ($mysqli->next_result()) {;} // flush multi_queries
$mysqli->query(" SQL statement #1 ; ") // now executed!
$mysqli->query(" SQL statement #2 ; ") // now executed!
$mysqli->query(" SQL statement #3 ; ") // now executed!
$mysqli->query(" SQL statement #4 ; ") // now executed!
?>

To be able to execute a $mysqli->query() after a $mysqli->multi_query() for MySQL > 5.3, I updated the code of jcn50 by this one :

<?php
    // WORKING CODE:
    $mysqli->multi_query(" Many SQL queries ; "); // OK

    while ($mysqli->next_result()) // flush multi_queries
    {
        if (!$mysqli->more_results()) break;
    }

    $mysqli->query(" SQL statement #1 ; ") // now executed!
    $mysqli->query(" SQL statement #2 ; ") // now executed!
    $mysqli->query(" SQL statement #3 ; ") // now executed!
    $mysqli->query(" SQL statement #4 ; ") // now executed!
?>

Note that you need to use this function to call Stored Procedures!

If you experience "lost connection to MySQL server" errors with your Stored Procedure calls then you did not fetch the 'OK' (or 'ERR') message, which is a second result-set from a Stored Procedure call. You have to fetch that result to have no problems with subsequent queries.

Bad example, will FAIL now and then on subsequent calls:
<?php
$sQuery='CALL exampleSP('param')';
if(!mysqli_multi_query($this->sqlLink,$sQuery))
  $this->queryError();
$this->sqlResult=mysqli_store_result($this->sqlLink);
?>

Working example:
<?php
$sQuery='CALL exampleSP('param')';
if(!mysqli_multi_query($this->sqlLink,$sQuery))
  $this->queryError();
$this->sqlResult=mysqli_store_result($this->sqlLink);

if(mysqli_more_results($this->sqlLink))
  while(mysqli_next_result($this->sqlLink));
?>

Of course you can do more with the multiple results then just throwing them away, but for most this will suffice. You could for example make an "sp" function which will kill the 2nd 'ok' result.

This nasty 'OK'-message made me spend hours trying to figure out why MySQL server was logging warnings with 'bad packets from client' and PHP mysql_error() with 'Connection lost'. It's a shame the mysqli library does catch this by just doing it for you.

Here are more details about error checking and return values from multi_query().  Testing shows that there are some mysqli properties to check for each result:

affected_rows
errno
error
insert_id
warning_count

If error or errno are not empty then the remaining queries did not return anything, even though error and errno will appear to be empty if processing further results is continued.

Also note that get_warnings() will not work with multi_query().  It can only be used after looping through all results, and it will only get the warnings for the last one of the queries and not for any others.  If you need to see or log query warning strings then you must not use multi_query(), because you can only see the warning_count value.

I was developing my own CMS and I was having problem with attaching the database' sql file. I thought mysqli_multi_query got bugs where it crashes my MySQL server. I tried to report the bug but it showed that it has duplicate bug reports of other developers. To my surprise, mysqli_multi_query needs to bother with result even if there's none.

I finally got it working when I copied the sample and removed somethings. Here is what it looked liked

<?php
$link = mysqli_connect("localhost", "my_user", "my_password", "world");

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

$query  = "CREATE TABLE....;...;... blah blah blah;...";

/* execute multi query */
if (mysqli_multi_query($link, $query)) {
   do {
       /* store first result set */
       if ($result = mysqli_store_result($link)) {
           //do nothing since there's nothing to handle
           mysqli_free_result($result);
       }
       /* print divider */
       if (mysqli_more_results($link)) {
           //I just kept this since it seems useful
           //try removing and see for yourself
       }
   } while (mysqli_next_result($link));
}

/* close connection */
mysqli_close($link);
?>

bottom-line: I think mysql_multi_query should only be used for attaching a database. it's hard to handle results from 'SELECT' statements inside a single while loop.

Following code can be used to resolve 
mysqli::next_result(): There is no next result set. Please, call mysqli_more_results()/mysqli::more_results() to check whether to call this function/method 

        $query = "SELECT SOME_COLUMN FROM SOME_TABLE_NAME;";
        $query .= "SELECT SOME_OTHER_COLUMN FROM SOME_TABLE_NAME";
        /* execute multi query */
        if (mysqli_multi_query($this->conn, $query)) {
            $i = true;
            do {
                /* store first result set */
                if ($result = mysqli_store_result($this->conn)) {
                    while ($row = mysqli_fetch_row($result)) {
                        printf("%s\n", $row[0]);
                    }
                    mysqli_free_result($result);
                }
                /* print divider */
                if (mysqli_more_results($this->conn)) {
                    $i = true;
                    printf("-----------------\n");
                } else {
                    $i = false;
                }
            } while ($i && mysqli_next_result($this->conn));
        }

You can use prepared statements on stored procedures.

You just need to flush all the subsequent result sets before closing the statement... so:

$mysqli_stmt = $mysqli->prepare(....);

... bind, execute, bind, fetch ...

while($mysqli->more_results())
{
    $mysqli->next_result();
    $discard = $mysqli->store_result();
}

$mysqli_stmt->close();

Hope that helps :o)

Use generator. 
PHP 5.5.0
<?php
// Quick multiQuery func.
function multiQuery( mysqli $mysqli, $query ) {
    if ($mysqli->multi_query( $query )) {
    do {
        if ($result = $mysqli->store_result()) {
            while ($row = $result->fetch_row()) {
                foreach ($row as $key => $value) yield $key => $value;
            }
            $result->free();
        }
    } while( $mysqli->more_results() && $mysqli->next_result() );
    }
}

$query = "OPTIMIZE TABLE `question`;" .
         "LOCK TABLES `question` READ;" . 
         "SELECT * FROM `question` WHERE `questionid`=2;" . 
         "SELECT * FROM `question` WHERE `questionid`=7;" . 
         "SELECT * FROM `question` WHERE `questionid`=8;" . 
         "SELECT * FROM `question` WHERE `questionid`=9;" . 
         "SELECT * FROM `question` WHERE `questionid`=11;" . 
         "SELECT * FROM `question` WHERE `questionid`=12;" . 
         "UNLOCK TABLES;" . 
         "TRUNCATE TABLE `question`;";

$mysqli = new mysqli('localhost', 'user', 'pswd', 'dbnm');
$mysqli->set_charset("cp1251");

// result
foreach ( multiQuery($mysqli, $query) as $key => $value ) {
    echo $key, $value, PHP_EOL;
}

?>
Good luck!

If you want to create a table with triggers, procedures or functions in one multiline query you may stuck with a error -
#1064 - You have an error in your SQL syntax; xxx corresponds to your MySQL server version for the right syntax to use near 'DELIMITER' at line 1

The solution is very simple - don't use DELIMITER keyword at all! So, instead of :

DELIMITER |
CREATE TRIGGER $dbName.$iname BEFORE INSERT ON $table FOR EACH ROW
BEGIN
    <body>
EOT|
DELIMITER ;

just use :

CREATE TRIGGER $dbName.$iname BEFORE INSERT ON $table FOR EACH ROW
BEGIN
    <body>
EOT;

For more information read answers at StackOverflow for question #5311141 

http://stackoverflow.com/questions/5311141/how-to-execute-mysql-command-delimiter

I appreciate the advice from crmccar at gmail dot com regarding the proper way to check for errors, but I would get an error with his/her code. I fixed it by changing the code a little:

<?php
$sql = file_get_contents( 'sql/test_' . $id . '_data.sql');

$query_array = explode(';', $sql);

// Run the SQL
$i = 0;
if( $this->mysqli->multi_query( $sql ) )
{
    do {
        $this->mysqli->next_result();

        $i++;
    }
    while( $this->mysqli->more_results() ); 
}

if( $this->mysqli->errno )
{
    die(
        '<h1>ERROR</h1>
        Query #' . ( $i + 1 ) . ' of <b>test_' . $id . '_data.sql</b>:<br /><br />
        <pre>' . $query_array[ $i ] . '</pre><br /><br /> 
        <span style="color:red;">' . $this->mysqli->error . '</span>'
    );
}
?>

I'd like to reinforce the correct way of catching errors from the queries executed by multi_query(), since the manual's examples don't show it and it's easy to lose UPDATEs, INSERTs, etc. without knowing it.

$mysqli->next_result() will return false if it runs out of statements OR if the next statement has an error. Therefore, it's important to check for errors when the loop ends. Also, I believe it's useful to know when and where the loop broke, so consider the following code:

<?php
$statements = array("INSERT INTO tablename VALUES ('1', 'one')", "INSERT INTO tablename VALUES ('2', 'two')");
if ($mysqli->multi_query(implode(';', $statements))) {
    $i = 0;
    do {
        $i++;
    } while ($mysqli->next_result());
}
if ($mysqli->errno) {
    echo "Batch execution prematurely ended on statement $i.\n";
    var_dump($statements[$i], $mysqli->error);
}
?>

The IF statement on the multi_query() call checks the first result, because next_result() starts at the second.

If your second or late query returns no result or even if your query is not a valid SQL query, more_results(); returns true in any case.

Be sure to not send a set of queries that are larger than max_allowed_packet size on your MySQL server. If you do, you'll get an error like: 
Mysql Error (1153): Got a packet bigger than 'max_allowed_packet' bytes

To see your MySQL size limitation, run the following query: show variables like 'max_allowed_packet';

or see http://dev.mysql.com/doc/refman/5.1/en/packet-too-large.html

Follow-up about MySQL warnings with multi_query():

Although get_warnings() will not work with multi_query(), this doesn't totally prevent retrieval of the warnings.  The workaround is to splice ';SHOW WARNINGS;' between every query.  This is necessary because the warning count(s) won't be returned until after the queries are already sent and executed.

With that little workaround, every 2nd result set will be a warning list from the previous query.  This adds some overhead that isn't necessary in production, but can be vital for debugging any use of multi_query() during development.

Conclusion: If you need to see or log query warning strings then you can either avoid multi_query() or you can manually pull the warning list after every query.

Getting "Error: Commands out of sync; you can't run this command now" after running a multi-query? Make sure you've cleared out the queue of results.

Here's what I've used to discard all subsequent results from a multi-query:

<?php
while($dbLink->more_results() && $dbLink->next_result()) {
    $extraResult = $dbLink->use_result();
    if($extraResult instanceof mysqli_result){
        $extraResult->free();
    }
}

?>

To get the affected/selected row count from all queries

$q = "UPDATE `Review` SET `order` = 1 WHERE id = 600;" // aff 1
       .  "UPDATE `Review` SET `order` = 600 WHERE id = 1;" //aff 1
    . "SELECT 0;" //for testing, aff rows == -1
                    ;
    
    $affcnt = 0;
    $rowcnt = 0;
        
    $res = $db->multi_query($q);
    if($res == false)
        Lib::throw( $q . "\n[" . $db->errno . "]\n" . $db->error . "\n" );    
    do
    {
        $affcnt += $db->affected_rows;
        if( isset($res->num_rows) )
            $rowcnt += $res->num_rows;
    }
    while( $db->more_results() && $res = $db->next_result() );
    //IMPORTANT: call more_results First!, THEN next_result to get new data.
        
    return $res;

This example shows how to read data from multiple stored procedures. Here I have two stored procedures proc1() and proc2() and retrieve their data into 2D array:

<?php

$db=new mysqli(...);

$sql="CALL proc1(...); CALL proc2(...);";

$procs=[]; //outer array for resultsets (tables)
$cols=[]; //inner array for columns (fields)

if($db->multi_query($sql))
{
  do
  {
    $db->next_result();
    if($rst=$db->use_result())
    {
      while($row=$rst->fetch_row())
      {
          $cols[]=$row[0]; //fetch 1st column value
          $cols[]=$row[1]; //fetch 2nd column value
      }
      $procs[]=$cols; //add cols to procedures array
    }
  }
  while($this->db->more_results());
}

?>

if you don't iterate through all results you get "server has gone away" error message ...

to resolve this, in php 5.2 it is enough to use

<?php
  // ok for php 5.2
  while ($mysqli->next_result());
?>

to drop unwanted results, but in php 5.3 using only this throws

mysqli::next_result(): There is no next result set. Please, call mysqli_more_results()/mysqli::more_results() to check whether to call this function/method

so it should be replaced with

<?php
  // ok for php 5.3
  while ($mysqli->more_results() && $mysqli->next_result());
?>

I also tried but failed:

<?php

  // can create infinite look in some cases
  while ($mysqli->more_results())
    $mysqli->next_result();

  // also throws error in some cases
  if ($mysqli->more_results())
    while ($mysqli->next_result());

?>

It's very important that after executing mysqli_multi_query you have first process the resultsets before sending any another statement to the server, otherwise your
socket is still blocked.

Please note that even if your multi statement doesn't contain SELECT queries, the server will send result packages containing errorcodes (or OK packet) for single statements.

mysqli_multi_query handles MySQL Transaction on InnoDB's :-)

<?php

$mysqli  = mysqli_connect( "localhost", "owner", "pass", "db", 3306, "/var/lib/mysql/mysql.sock" );

$QUERY = <<<EOT
START TRANSACTION;
SELECT @lng:=IF( STRCMP(`main_lang`,'de'), 'en', 'de' )
FROM `main_data` WHERE  ( `main_activ` LIKE 1 ) ORDER BY `main_id` ASC;
SELECT `main_id`, `main_type`, `main_title`, `main_body`, `main_modified`, `main_posted`
FROM `main_data`
WHERE ( `main_type` RLIKE "news|about" AND `main_lang` LIKE @lng AND `main_activ` LIKE 1 )
ORDER BY `main_type` ASC;
COMMIT;
EOT;

$query = mysqli_multi_query( $mysqli, $QUERY ) or die( mysqli_error( $mysqli ) );

if( $query )
{
  do {
    if( $result = mysqli_store_result( $mysqli ) )
    {
      $subresult = mysqli_fetch_assoc( $result );
      if( ! isset( $subresult['main_id'] ) )
        continue;

      foreach( $subresult AS $k => $v )
      {
        var_dump( $k , $v );
      }
    }
  } while ( mysqli_next_result( $mysqli ) );
}

mysqli_close( $mysqli );

?>

Multi-queries open the potential for a SQL injection. 

The often cited "fallback" loop:

<?php
while ( $db->more_results() and $db->next_result() ) {
  $rs = $db->use_result();
  if( $rs instanceof \mysqli_result ) {
      $rs->free();
}
?>

certainly will avoid the dreaded error 2014 "Commands out of sync; you can't run this command now" error. However, that technique will completely disregard the fact that any excess result sets are a likely indication of an infiltrated system.

Instead, it may be wise to tightly manage the correct number of expected, individual result sets and throw an exception of more are received.

However, it's important to understand that any closing comment (which might have been appended as one defense against command appending) will result in an EXTRA, EMPTY result set.

Example:

SELECT SQL_CALC_FOUND_ROWS * FROM `table` LIMIT 10; SELECT FOUND_ROWS(); --

will produce THREE result sets:

#1 - the ten data rows,
#2 - the overall row count,
#3 - an empty result set, where: FALSE === $db->use_result(), even though it had been TRUE === ($db->more_results() and $db->next_result() ) .

Please note that there is no need for the semicolon after the last query. That wasted more than hour of my time...

If you're importing a sql-file with triggers, functions, stored procedures and other stuff, you'll might be using DELIMITER in MySQL.
Notice: This function assumes that all delimiters are on it's own line, and that "DELIMITER" are in all caps.

<?php
function mysqli_multi_query_file($mysqli, $filename) {
    $sql = file_get_contents($filename);
    // remove comments
    $sql = preg_replace('#/\*.*?\*/#s', '', $sql);
    $sql = preg_replace('/^-- .*[\r\n]*/m', '', $sql);
    if (preg_match_all('/^DELIMITER\s+(\S+)$/m', $sql, $matches, PREG_SET_ORDER | PREG_OFFSET_CAPTURE)) {
        $prev = null;
        $index = 0;
        foreach ($matches as $match) {
            $sqlPart = substr($sql, $index, $match[0][1] - $index);
            // move cursor after the delimiter
            $index = $match[0][1] + strlen($match[0][0]);
            if ($prev && $prev[1][0] != ';') {
                $sqlPart = explode($prev[1][0], $sqlPart);
                foreach ($sqlPart as $part) {
                    if (trim($part)) { // no empty queries
                        $mysqli->query($part);
                    }
                }
            } else {
                if (trim($sqlPart)) { // no empty queries
                    $mysqli->multi_query($sqlPart);
                    while ($mysqli->next_result()) {;}
                }
            }
            $prev = $match;
        }
        // run the sql after the last delimiter
        $sqlPart = substr($sql, $index, strlen($sql)-$index);
        if ($prev && $prev[1][0] != ';') {
            $sqlPart = explode($prev[1][0], $sqlPart);
            foreach ($sqlPart as $part) {
                if (trim($part)) {
                    $mysqli->query($part);
                }
            }
        } else {
            if (trim($sqlPart)) {
                $mysqli->multi_query($sqlPart);
                while ($mysqli->next_result()) {;}
            }
        }
    } else {
        $mysqli->multi_query($sql);
        while ($mysqli->next_result()) {;}
    }
}
?>