PDO::prepare

(PHP 5 >= 5.1.0, PHP 7, PHP 8, PHP 8,PECL pdo >= 0.1.0)

PDO::prepare — Bereitet eine Anweisung zur Ausführung vor und liefert ein Anweisungsobjekt

Beschreibung

public PDO::prepare(string $query, array $options = []): PDOStatement|false

Bereitet eine SQL-Anweisung vor, die von der Methode PDOStatement::execute() ausgeführt werden soll. Die Vorlage für eine Anweisung kann null oder mehr benannte (:name) oder mit Fragezeichen (?) versehene Platzhalter für Parameter enthalten, die bei der Ausführung der Anweisung durch reale Werte ersetzt werden. Benannte und Fragezeichen-Parameter dürfen nicht gleichzeitig in derselben Anweisungsvorlage verwendet werden, sondern nur eine der beiden Varianten. Diese Parameter werden verwendet, um die Benutzereingaben zu binden. Benutzerangaben sollten niemals direkt in die Abfrage aufgenommen werden.

Für jeden Wert, der beim Aufruf von PDOStatement::execute() an die Anweisung übergeben werden soll, muss ein eindeutiger Platzhalter angegeben werden. Ein benannter Platzhalter darf nur dann mehrfach verwendet werden, wenn der Emulationsmodus aktiviert ist.

Hinweis:
Die Platzhalter für die Parameter können nur ein vollständiges Datenliteral darstellen. Es ist nicht möglich, einen Teil eines Literals, ein Schlüsselwort, einen Bezeichner oder einen beliebigen Teil einer Abfrage an einen Parameter zu binden. So können zum Beispiel in einer IN()-Klausel einer SQL-Anweisung nicht mehrere Werte an einen einzigen Parameter gebunden werden.

Mittels PDO::prepare() und PDOStatement::execute() kann der Treiber bei Anweisungen, die mehrfach mit unterschiedlichen Parameterwerten ausgeführt werden, die Leistung einer Anwendung optimieren, indem er die Zwischenspeicherung des Abfrageplans und der Metainformationen auf Client- und/oder Serverseite aushandelt. Außerdem trägt dies dazu bei, Angriffe durch SQL-Injection zu verhindern, weil die Parameter nicht mehr manuell maskiert und in Anführungszeichen gesetzt werden müssen.

Bei Treibern, die diese nicht unterstützen, emuliert PDO vorbereitete Anweisungen/gebundene Parameter und kann außerdem benannte oder mit Fragezeichen versehene Parametermarkierungen in eine geeignetere Form umwandeln, wenn der Treiber zwar die eine, nicht aber die andere Form unterstützt.

Hinweis: Der Parser, der für emulierte vorbereitete Anweisungen verwendet wird und die benannten oder durch Fragezeichen angegebenen Parameter umschreibt, unterstützt die nicht standardmäßige Maskierung einfacher und doppelter Anführungszeichen durch Backslashes. Dies hat zur Folge, dass abschließende Anführungszeichen, denen ein Backslash unmittelbar vorausgeht, nicht als solche erkannt werden, was dazu führen kann, dass Parameter falsch erkannt werden und die vorbereitete Anweisung bei ihrer Ausführung fehlschlägt. Um dies zu umgehen, sollten für solche SQL-Abfragen keine emulierten vorbereiteten Anweisungen verwendet werden. Außerdem sollte ein vom Treiber nativ unterstützter Parameterstil verwendet werden, um ein Umschreiben der Parameter zu vermeiden.

Seit PHP 7.4.0 können Fragezeichen durch Verdoppeln maskiert werden. Das bedeutet, dass die Zeichenkette ?? beim Senden der Abfrage an die Datenbank in ? übersetzt wird.

Parameter-Liste

query: Dies muss eine für den jeweiligen Datenbankserver gültige Vorlage für eine SQL-Anweisung sein.
options: Dieses Array enthält ein oder mehrere Schlüssel=>Wert-Paare, um die Werte der Attribute des von dieser Methode zurückgegebenen PDOStatement-Objekts zu setzen. Am häufigsten wird dies verwendet, um den Wert von PDO::ATTR_CURSOR für einen scrollbaren Cursor auf PDO::CURSOR_SCROLL zu setzen. Einige Treiber haben treiberspezifische Optionen, die während der Vorbereitung gesetzt werden können.

Rückgabewerte

Wenn der Datenbankserver die Anweisung erfolgreich vorbereitet hat, gibt PDO::prepare() ein PDOStatement-Objekt zurück. Schlägt die Vorbereitung fehl, gibt PDO::prepare() false zurück oder löst eine PDOException aus (abhängig von der Fehlerbehandlung).

Hinweis:
Da emulierte vorbereitete Anweisungen nicht mit dem Datenbankserver kommunizieren, überprüft PDO::prepare() die Anweisung nicht.

Fehler/Exceptions

Gibt einen Fehler der Stufe E_WARNING aus, wenn das Attribut PDO::ATTR_ERRMODE auf PDO::ERRMODE_WARNING gesetzt ist.

Löst eine PDOException aus, wenn das Attribut PDO::ATTR_ERRMODE auf PDO::ERRMODE_EXCEPTION gesetzt ist.

Beispiele

Beispiel #1 Vorlage für eine SQL-Anweisung mit benannten Parametern

<?php
/* Ausführen einer vorbereiteten Anweisung durch Übergabe eines Arrays von Werten */
$sql = 'SELECT name, colour, calories
    FROM fruit
    WHERE calories < :calories AND colour = :colour';
$sth = $dbh->prepare($sql, [PDO::ATTR_CURSOR => PDO::CURSOR_FWDONLY]);
$sth->execute(['calories' => 150, 'colour' => 'red']);
$red = $sth->fetchAll();
/* Den Array-Schlüsseln kann auch ein Doppelpunkt ":" vorangestellt werden (optional) */
$sth->execute([':calories' => 175, ':colour' => 'yellow']);
$yellow = $sth->fetchAll();
?>

Beispiel #2 Vorlage für eine SQL-Anweisung mit Fragezeichen als Platzhalter

<?php
/* Ausführen einer vorbereiteten Anweisung durch Übergabe eines Arrays von Werten */
$sth = $dbh->prepare('SELECT name, colour, calories
    FROM fruit
    WHERE calories < ? AND colour = ?');
$sth->execute([150, 'red']);
$red = $sth->fetchAll();
$sth->execute([175, 'yellow']);
$yellow = $sth->fetchAll();
?>

Beispiel #3 Vorlage für eine SQL-Anweisung mit maskierten Fragezeichen

<?php
/* Hinweis: dies ist nur bei PostgreSQL-Datenbanken möglich */
$sth = $dbh->prepare('SELECT * FROM issues WHERE tag::jsonb ?? ?');
$sth->execute(['feature']);
$featureIssues = $sth->fetchAll();
$sth->execute(['performance']);
$performanceIssues = $sth->fetchAll();
?>

Siehe auch

PDO::exec() - Führt ein SQL-Statement aus und liefert die Anzahl der betroffenen Zeilen
PDO::query() - Bereitet eine SQL-Anweisung ohne Platzhalter vor und führt sie aus
PDOStatement::execute() - Führt ein Prepared Statement aus

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User Contributed Notes 17 notes

down

185

Anonymous ¶

12 years ago

To those wondering why adding quotes to around a placeholder is wrong, and why you can't use placeholders for table or column names:

There is a common misconception about how the placeholders in prepared statements work: they are not simply substituted in as (escaped) strings, and the resulting SQL executed. Instead, a DBMS asked to "prepare" a statement comes up with a complete query plan for how it would execute that query, including which tables and indexes it would use, which will be the same regardless of how you fill in the placeholders.

The plan for "SELECT name FROM my_table WHERE id = :value" will be the same whatever you substitute for ":value", but the seemingly similar "SELECT name FROM :table WHERE id = :value" cannot be planned, because the DBMS has no idea what table you're actually going to select from.

Even when using "emulated prepares", PDO cannot let you use placeholders anywhere, because it would have to work out what you meant: does "Select :foo From some_table" mean ":foo" is going to be a column reference, or a literal string?

When your query is using a dynamic column reference, you should be explicitly white-listing the columns you know to exist on the table, e.g. using a switch statement with an exception thrown in the default: clause.

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Simon Le Pine ¶

12 years ago

Hi All,

First time posting to php.net, a little nervous.

After a bunch of searching I've learned 2 things about prepared statements:
1.) It fails if you enclose in a single quote (')
This fails: "SELECT * FROM users WHERE email=':email'"
This works: "SELECT * FROM users WHERE email=:email"
2.) You cannot search with a prepared statement
This fails: "SELECT * FROM users WHERE :search=:email"
This succeeds: "SELECT * FROM users WHERE $search=:email"

In my case I allow the user to enter their username or email, determine which they've entered and set $search to "username" or "email". As this value is not entered by the user there is no potential for SQL injection and thus safe to use as I have done.

Hope that saves someone else from a lot of searching.

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daniel dot egeberg at gmail dot com ¶

16 years ago

You can also pass an array of values to PDOStatement::execute(). This is also secured against SQL injection. You don't necessarily have to use bindParam() or bindValue().

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bg at enativ dot com ¶

11 years ago

if you run queries in a loop, don't include $pdo->prepare() inside the loop, it will save you some resources (and time).

prepare statement inside loop:
for($i=0; $i<1000; $i++) {
    $rs = $pdo->prepare("SELECT `id` FROM `admins` WHERE `groupID` = :groupID AND `id` <> :id");
    $rs->execute([':groupID' => $group, ':id' => $id]);
}

// took 0.066626071929932 microseconds

prepare statement outside loop:
$rs = $pdo->prepare("SELECT `id` FROM `admins` WHERE `groupID` = :groupID AND `id` <> :id");
for($i=0; $i<1000; $i++) {
    $rs->execute([':groupID' => $group, ':id' => $id]);
}

// took 0.064448118209839 microseconds

for 1,000 (simple) queries it took 0.002 microseconds less.
not much, but it worth mention.

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admin at wdfa dot co dot uk ¶

16 years ago

Note on the SQL injection properties of prepared statements.

Prepared statements only project you from SQL injection IF you use the bindParam or bindValue option.

For example if you have a table called users with two fields, username and email and someone updates their username you might run

UPDATE `users` SET `user`='$var'

where $var would be the user submitted text. 

Now if you did 
<?php
$a=new PDO("mysql:host=localhost;dbname=database;","root","");
$b=$a->prepare("UPDATE `users` SET user='$var'");
$b->execute();
?>

and the user had entered  User', email='test for a test the injection would occur and the email would be updated to test as well as the user being updated to User.

Using bindParam as follows
 <?php
$var="User', email='test";
$a=new PDO("mysql:host=localhost;dbname=database;","root","");
$b=$a->prepare("UPDATE `users` SET user=:var");
$b->bindParam(":var",$var);
$b->execute();
?>

The sql would be escaped and update the username to User', email='test'

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theking2 at king dot ma ¶

2 years ago

There are restrictions on the placeholder string. In the following code the first execute fails with a SQLSTATE[HY093]. It is not clear exactly what characters are allowed.

<?php declare(strict_types=1);

$db = new \PDO("mysql:hostname=localhost;dbname=minidwh", "minidwh", "Meisterstueck!");
$db->query("SET NAMES 'utf8mb4'");

$db->query("DROP TABLE IF EXISTS `äëïöüß`");
$db->query("CREATE TABLE `äëïöüß` ( `id` INT NOT NULL AUTO_INCREMENT, PRIMARY KEY (`id`) ) ENGINE = ARIA;");
$db->query("ALTER TABLE `äëïöüß` ADD COLUMN `äëïöüß` TEXT NULL");
try {
  $stmt = $db->prepare("INSERT INTO `äëïöüß` (`äëïöüß`) VALUES (:äëïöüß)");
  $result = $stmt->execute([':äëïöüß' => 'test1']);
} catch (\PDOException $e) {
  echo $e->getMessage() . '<BR>';
}

try {
  $stmt = $db->prepare("INSERT INTO `äëïöüß` (`äëïöüß`) VALUES (?)");
  $result = $stmt->execute(['test2']);
} catch (\PDOException $e) {
  echo $e->getMessage() . '<BR>';
}

try {
  $stmt = $db->prepare("INSERT INTO `äëïöüß` (`äëïöüß`) VALUES (:column)");
  $result = $stmt->execute([':column' => 'test3']);
} catch (\PDOException $e) {
  echo $e->getMessage() . '<BR>';
}

try {
  $stmt = $db->prepare("INSERT INTO `äëïöüß` (`äëïöüß`) VALUES (:column)");
  $stmt->bindValue(':column', 'test4');
  $result = $stmt->execute();
} catch (\PDOException $e) {
  echo $e->getMessage() . '<BR>';
}

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Mark Simon ¶

8 years ago

Many students are tempted to add single quotes around string place holders in the SQL statement, since that’s what they normally do around strings in SQL and PHP.

I have to explain:

Quotes are not part of the string — they are used to construct a string in the coding language. If you are creating a string literal in SQL or PHP, then it must indeed be quoted. If the string has already been created, and is being passed on, then additional quotes would be wrong at best, and mis-interpreted at worst.

In prepared place holders, think of place holders as variables, which, whether they are strings or other values, are always written without quotes.

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public at grik dot net ¶

13 years ago

With PDO_MYSQL you need to remember about the PDO::ATTR_EMULATE_PREPARES option.

The default value is TRUE, like
$dbh->setAttribute(PDO::ATTR_EMULATE_PREPARES,true); 

This means that no prepared statement is created with $dbh->prepare() call. With exec() call PDO replaces the placeholders with values itself and sends MySQL a generic query string.

The first consequence is that the call  $dbh->prepare('garbage');
reports no error. You will get an SQL error during the $dbh->exec() call.
The second one is the SQL injection risk in special cases, like using a placeholder for the table name.

The reason for emulation is a poor performance of MySQL with prepared statements. Emulation works significantly faster.

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Robin ¶

15 years ago

Use prepared statements to ensure integrity of binary data during storage and retrieval. Escaping/quoting by f.e. sqlite_escape_string() or PDO::quote() is NOT suited for binary data - only for strings of text.

A simple test verifies perfect storage and retrieval with prepared statements:

<?php

$num_values = 10000;

$db = new pdo( 'sqlite::memory:' );

$db->exec( 'CREATE TABLE data (binary BLOB(512));' );

// generate plenty of troublesome, binary data
for( $i = 0; $i < $num_values; $i++ )
{
    for( $val = null, $c = 0; $c < 512/16; $c++ )
        $val .= md5( mt_rand(), true );
    @$binary[] = $val;
}

// insert each value by prepared statement
for( $i = 0; $i < $num_values; $i++ )
    $db->prepare( 'INSERT INTO data VALUES (?);' )->execute( array($binary[$i]) );

// fetch the entire row
$data = $db->query( 'SELECT binary FROM data;' )->fetchAll( PDO::FETCH_COLUMN );

// compare with original array, noting any mismatch
for( $i = 0; $i < $num_values; $i++ )
    if( $data[$i] != $binary[$i] ) echo "[$i] mismatch\n";

$db = null;

?>

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php dot chaska at xoxy dot net ¶

12 years ago

Note that for Postgres, even though Postgres does support prepared statements, PHP's PDO driver NEVER sends the prepared statement to the Postgres server in advance of the call to PDO::execute().  

Therefore, PDO::prepare() will never throw an error for things like faulty SQL syntax.  

It also means the server will not parse and plan the SQL until the first time PDO::execute() is called, which may or may not adversely affect your optimization plans.

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php at bagnara dot org ¶

9 months ago

As mentioned above, column and table identifiers cannot be passed as parameters in prepared queries. PDO also does not provide a method to escape and quote an identifier. The following method is what I use to escape and quote an identifier. Note that $this->pdo is a PDO object.

<?php
    /**
     * Escape and quote an identifier.
     * 
     * @param string $identifier Column or table name to escape and quote
     * @param string $quoteWith Database dependent, default backtick
     * @return string 
     */
    public function
    quoteIdentifier( string $identifier, $quoteWith = '`' )  :  string
    {
        $s = $this->pdo->quote( $identifier ) ;  // escaped and quoted
        $s = trim( $s, $s[0] ) ;            // remove the quotes, assumes open and closing the same
        $s = $quoteWith . $s . $quoteWith ; // add new quote
        return $s ;
    }
?>

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roth at egotec dot com ¶

19 years ago

Attention using MySQL and prepared statements.
Using a placeholder multiple times inside a statement doesn't work. PDO just translates the first occurance und leaves the second one as is.

select id,name from demo_de where name LIKE :name OR name=:name

You have to use

select id,name from demo_de where name LIKE :name OR name=:name2

and bind name two times. I don't know if other databases (for example Oracle or MSSQL) support multiple occurances. If that's the fact, then the PDO behaviour for MySQL should be changed.

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pbakhuis ¶

11 years ago

Noteworthy in my opinion is that if you prepare a statement but do not bind a value to the markers it will insert null by default. e.g.
<?php
/** @var PDO $db */
$prep = $db->prepare('INSERT INTO item(title, link) VALUES(:title, :link)');
$prep->execute();
?>
Will attempt to insert null, null into the item table.

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-1

machitgarha at outlook dot com ¶

8 years ago

Hello everyone.

I want to note that it doesn't matter where you are using a variable inside the query directly, that is not secure against SQL injections (unless performing a long security operation).

The following example is insecure against SQL injections:

<?php

$statement = $databaseConnection->prepare("SELECT * FROM `$_POST['table']` WHERE $_POST['search_for']=:search");
$statement->bindParam(":search", $search);
$search = 18; // For example
$statement->execute();

?>

If an attacker pass '1;-- ' as input named 'search_for', he is not a very bad attacker; because he didn't delete your data! In the above example, an attacker can do anything with connected database (unless you have restricted the connected user). Unfortunately, as Simon Le Pine mentioned, you cannot use prepared statements as other parts of a query; just can be used to search in indexes.

Hope this helps from loosing some data.
Sorry for my a bit weak English!

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-2

orrd101 at gmail dot com ¶

13 years ago

Don't just automatically use prepare() for all of your queries.

If you are only submitting one query, using PDO::query() with PDO::quote() is much faster (about 3x faster in my test results with MySQL).  A prepared query is only faster if you are submitting thousands of identical queries at once (with different data).

If you Google for performance comparisons you will find that this is generally consistently the case, or you can write some code and do your own comparison for your particular configuration and query scenario. But generally PDO::query() will always be faster except when submitting a large number of identical queries.  Prepared queries do have the advantage of escaping the data for you, so you have to be sure to use quote() when using query().

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-2

Hayley Watson ¶

12 years ago

It is possible to prepare in advance several statements against a single connection. As long as that connection remains open the statements can be executed and fetched from as often as you like in any order; their "prepare-execute-fetch" steps can be interleaved in whichever way is best.

So if you're likely to be using several statements often (perhaps within a loop of transactions), you may like to consider preparing all the statements you'll be using up front.

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-4

ak_9jsz ¶

17 years ago

Using cursors doesn't work with SQLite 3.5.9. I get an error message when it gets to the execute() method.

Some of you might be saying "duh!" but i was surprised to see TRIGGER support in SQLite, so i had to try. :)

I wanted to use Absolute referencing on a Scrollable cursor and i only wanted one column of data. So i used this instead of a cursor.

<?php

$dbo = new PDO('sqlite:tdb');
$sql = 'SELECT F1, F2 FROM tblA WHERE F1 <> "A";';
$res = $dbo->prepare($sql);
$res->execute();
$resColumn = $res->fetchAll(PDO::FETCH_COLUMN, 0);

for($r=0;$r<=3;$r++)
    echo 'Row '. $r . ' returned: ' . $resColumn[$r] . "\n";

$dbo = null;
$res = null;
?>

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