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 = new mysqli("example.com", "user", "password", "database");
$result = $mysqli->query("SELECT 1; DROP TABLE mysql.user");
if (!$result) {
echo "Error executing query: (" . $mysqli->errno . ") " . $mysqli->error;
}
?>
The above example will output:
Error executing query: (1064) 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
