Consultas múltiples

    MySQL permite opcionalmente tener múltiples consultas en una sola cadena de consulta pero requiere una gestión especial.

    Las consultas múltiples o multiconsultas deben ser ejecutadas con la función mysqli::multi_query(). Las consultas individuales en la cadena de consulta están separadas por un punto y coma. Luego, todos los juegos de resultados devueltos por la ejecución de las consultas deben ser recuperados.

    El servidor MySQL permite tener consultas que devuelven juegos de resultados así como consultas que no devuelven ningún juego de resultados en la misma consulta múltiple.

    Ejemplo #1 Consultas múltiples

    <?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());

    El resultado del ejemplo sería:

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

    Desde un punto de vista de seguridad

    Las funciones mysqli::query() y mysqli::real_query() de la API no definen un flag de conexión necesario para la activación de las multiconsultas en el servidor. Una llamada adicional a la API es utilizada para las multiconsultas para reducir la probabilidad de inyección SQL accidental. Un atacante puede intentar agregar consultas como ; DROP DATABASE mysql o ; SELECT SLEEP(999). Si el atacante logra agregar este tipo de SQL en la cadena de consulta pero que mysqli::multi_query() no es utilizado, el servidor solo ejecutará la primera consulta, pero no la segunda que representa la consulta SQL maliciosa.

    Ejemplo #2 Inyección SQL

    <?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");

    El resultado del ejemplo sería:

    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

    Consultas preparadas

    El uso de consultas múltiples con consultas preparadas no es soportado.

    Ver también

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    User Contributed Notes 1 note

    up
    8
    velthuijsen
    6 years ago
    Suggested improvement(s) to example 1.

    reasons:
    Multi_query only returns a non false response if a data/result set is returned and only checks for the first query entered. Switching the first SELECT query with the INSERT query will result in a premature exit of the example with the message "Multi query failed: (0)".
    The example assumes that once the first query doesn't fail that the other queries have succeeded as well. Or rather it just exits without reporting that one of the queries after the first query failed seeing that if a query fails next_result returns false.

    The changes in the example comes after the creation of the string $sql.

    <?php
    $mysqli     = new mysqli("example.com", "user", "password", "database");
    if (    $mysqli->connect_errno) {
    echo     "Failed to connect to MySQL: (" . $mysqli->connect_errno . ") " . $mysqli->connect_error;
    }

    if (!    $mysqli->query("DROP TABLE IF EXISTS test") || !$mysqli->query("CREATE TABLE test(id INT)")) {
    echo     "Table creation failed: (" . $mysqli->errno . ") " . $mysqli->error;
    }

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

    // changes to example 1 start here

    // don't bother checking the result from multi_query since it will return false
    // if the first query does not return data even if the query itself succeeds.
    $mysqli->multi_query($sql);

    do     // while (true); // exit only on error or when there are no more queries to process
    {
    // check if query currently being processed hasn't failed
    if (0 !== $mysqli->errno)
    {
    echo     "Multi query failed: (" . $mysqli->errno . ") " . $mysqli->error;
    break;
    }

    // store and possibly process result of the query,
    // both store_result & use_result will return false
    // for queries that do not return results (INSERT for example)
    if(false !== ($res = $mysqli->store_result() )
    {
    var_dump($res->fetch_all(MYSQLI_ASSOC));
    $res->free();
    }

    // exit loop if there ar no more queries to process
    if (false === ($mysqli->more_results() )
    {
    break;
    }

    // get result of the next query to process
    // don't bother to check for success/failure of the result
    // since at the start of the loop there is an error check &
    // report block.
    $mysqli->next_result()

    } while (    true); // exit only on error or when there are no more queries to process
    ?>

    Note that the normal while ($mysqli->more_results() && $mysqli->next_result() has been replaced by two checks and while (true);
    This is due to the 'problem' that next_result will return false if the query in question failed.
    So one either needs to do one last check after the while loop to check if there was an error or one has to split up the different actions.
    The changes in the example do the splitting.
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