Multiple Statements

MySQL optionally allows having multiple statements in one statement string, but it requires special handling.

Multiple statements or multi queries must be executed with mysqli::multi_query(). The individual statements of the statement string are separated by semicolon. Then, all result sets returned by the executed statements must be fetched.

The MySQL server allows having statements that do return result sets and statements that do not return result sets in one multiple statement.

Example #1 Multiple Statements

<?php

mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
$mysqli = new mysqli("example.com", "user", "password", "database");

$mysqli->query("DROP TABLE IF EXISTS test");
$mysqli->query("CREATE TABLE test(id INT)");

$sql = "SELECT COUNT(*) AS _num FROM test;
        INSERT INTO test(id) VALUES (1); 
        SELECT COUNT(*) AS _num FROM test; ";

$mysqli->multi_query($sql);

do {
    if ($result = $mysqli->store_result()) {
        var_dump($result->fetch_all(MYSQLI_ASSOC));
        $result->free();
    }
} while ($mysqli->next_result());

The above example will output:

array(1) {
  [0]=>
  array(1) {
    ["_num"]=>
    string(1) "0"
  }
}
array(1) {
  [0]=>
  array(1) {
    ["_num"]=>
    string(1) "1"
  }
}

Security considerations

The API functions mysqli::query() and mysqli::real_query() do not set a connection flag necessary for activating multi queries in the server. An extra API call is used for multiple statements to reduce the damage of accidental SQL injection attacks. An attacker may try to add statements such as ; DROP DATABASE mysql or ; SELECT SLEEP(999). If the attacker succeeds in adding SQL to the statement string but mysqli::multi_query() is not used, the server will not execute the injected and malicious SQL statement.

Example #2 SQL Injection

<?php
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
$mysqli = new mysqli("example.com", "user", "password", "database");
$result = $mysqli->query("SELECT 1; DROP TABLE mysql.user");
?>

The above example will output:

PHP Fatal error:  Uncaught mysqli_sql_exception: You have an error in your SQL syntax; 
check the manual that corresponds to your MySQL server version for the right syntax to 
use near 'DROP TABLE mysql.user' at line 1

Prepared statements

Use of the multiple statement with prepared statements is not supported.

See also