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.
PDO::prepare
(PHP 5 >= 5.1.0, PHP 7, PECL pdo >= 0.1.0)
PDO::prepare — Prepara una sentencia para su ejecución y devuelve un objeto sentencia
Descripción
Prepara una sentencia SQL para ser ejecutada por el método PDOStatement::execute(). La sentencia SQL puede contener cero o más marcadores de parámetros con nombre (:name) o signos de interrogación (?) por los cuales los valores reales serán sustituidos cuando la sentencia sea ejecutada. No se pueden usar marcadores de parámetros con nombre y signos de interrogación en la misma sentencia SQL; se debe elegir uno de los dos estilos de parámetros. Se deben usar estos parámetros para sustituir cualquier dato de usuario, y no usarlos directamente en la consulta.
Se debe incluir un único marcador de parámetro para cada valor que se desee pasar a la sentencia cuando se llame a PDOStatement::execute(). No se puede usar un marcador de parámetro con nombre con el mismo nombre más de una vez en una sentencia preparada, a menos que el modo de emulación esté activado.
Nota:
Los marcadores de parámetros solamente pueden representar un literal de datos completo. No se pueden vincular usando parámetros una parte del literal, ni una palabra clave, ni un identificador, ni ninguna parte arbitraria de una consulta. Por ejemplo, no se puede vincular valores múltiples a un único parámetro en la cláusula IN() de una sentencia SQL.
Llamar a PDO::prepare() y a PDOStatement::execute() para sentencias que serán ejecutadas en múltiples ocasiones con diferentes parámetros optimiza el rendimiento de la aplicación permitiendo al driver negociar en lado del cliente y/o servidor el almacenamiento en caché del plan de consulta y meta información, y ayuda a prevenir inyecciones SQL eliminando la necesidad de entrecomillar manualmente los parámetros.
PDO emulará sentencias preparadas/parámetros de sustitución para drivers que no lo soporten nativamente, y puede reescribir el estilo de los parámetros de sustitución por una forma más apropiada, si el driver soporta un estilo pero no el otro.
Parámetros
-
statement -
Debe ser una plantilla de sentencia SQL válida para el servidor de base de datos destino.
-
driver_options -
Este array guarda uno o más pares clave=>valor para establecer el valor de los atributos del objeto PDOStatement que este método devuelve. Comúnmente se establece el valor PDO::ATTR_CURSOR a PDO::CURSOR_SCROLL para solicitar el cursor desplazable. Algunos drivers tienen opciones específicas que pueden ser establecidas en el momento de la preparación.
Valores devueltos
Si el servidor de la base de datos prepara con éxito la sentencia,
PDO::prepare() devuelve un objeto PDOStatement.
Si no es posible, PDO::prepare() devuelve FALSE
o emite una excepciónPDOException (dependiendo del manejo de errores).
Nota:
Las sentencias preparadas emuladas no se comunican con el servidor de la base de datos con lo cual PDO::prepare() no comprueba la sentencia.
Ejemplos
Ejemplo #1 Prepara una sentencia SQL con parámetros de sustitución nombrados
<?php
/* Ejecuta una sentencia preparada pasando un array de valores */
$sql = 'SELECT name, colour, calories
FROM fruit
WHERE calories < :calories AND colour = :colour';
$sth = $dbh->prepare($sql, array(PDO::ATTR_CURSOR => PDO::CURSOR_FWDONLY));
$sth->execute(array(':calories' => 150, ':colour' => 'red'));
$red = $sth->fetchAll();
$sth->execute(array(':calories' => 175, ':colour' => 'yellow'));
$yellow = $sth->fetchAll();
?>
Ejemplo #2 Prepara una sentencia SQL con parámetros de signos de interrogación
<?php
/* Ejecuta una sentencia preparada pasando un array de valores */
$sth = $dbh->prepare('SELECT name, colour, calories
FROM fruit
WHERE calories < ? AND colour = ?');
$sth->execute(array(150, 'red'));
$red = $sth->fetchAll();
$sth->execute(array(175, 'yellow'));
$yellow = $sth->fetchAll();
?>
Ver también
- PDO::exec() - Ejecuta una sentencia SQL y devuelve el número de filas afectadas
- PDO::query() - Ejecuta una sentencia SQL, devolviendo un conjunto de resultados como un objeto PDOStatement
- PDOStatement::execute() - Ejecuta una sentencia preparada
add a note
User Contributed Notes 26 notes
Anonymous ¶
6 years ago
daniel dot egeberg at gmail dot com ¶
10 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().
Simon Le Pine ¶
6 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 $search to "username" or "email". As this value is not entered by the user there is no potential for SQL injection and thus safe to use as I have done.
Hope that saves someone else from a lot of searching.
admin at wdfa dot co dot uk ¶
10 years ago
Note on the SQL injection properties of prepared statements.
Prepared statements only project you from SQL injection IF you use the bindParam or bindValue option.
For example if you have a table called users with two fields, username and email and someone updates their username you might run
UPDATE `users` SET `user`='$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'
bg at enativ dot com ¶
5 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.
public at grik dot net ¶
7 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.
pbakhuis ¶
5 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.
machitgarha at outlook dot com ¶
1 year 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!
php dot chaska at xoxy dot net ¶
5 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.
orrd101 at gmail dot com ¶
7 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().
Mark Simon ¶
2 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.
roth at egotec dot com ¶
12 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.
Hayley Watson ¶
6 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.
Robin ¶
9 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";
$db = null;
?>
johniskew ¶
12 years ago
If you need to create variable sql statements in a prepare statement...for example you may need to construct a sql query with zero, one, two, etc numbers of arguments...here is a way to do it without a lot of if/else statements needed to glue the sql together:
<?php
public function matchCriteria($field1=null,$field2=null,$field3=null) {
$db=DB::conn();
$sql=array();
$paramArray=array();
if(!empty($field1)) {
$sql[]='field1=?';
$paramArray[]=$field1;
}
if(!empty($field2)) {
$sql[]='field2=?';
$paramArray[]=$field2;
}
if(!empty($field3)) {
$sql[]='field3=?';
$paramArray[]=$field3;
}
$rs=$db->prepare('SELECT * FROM mytable'.(count($paramArray)>0 ? ' WHERE '.join(' AND ',$sql) : ''));
$result=$rs->execute($paramArray);
if($result) {
return $rs;
}
return false;
}
?>
ak_9jsz ¶
11 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;
$res = null;
?>
omidbahrami1990 at gmail dot com ¶
1 year ago
This Is A Secure Way To Sign in With pdo::prepare
--------------------------------------------------------
<?php
function secured_signin($username,$password)
{
try
{
$connection = new PDO("mysql:host=$dbhost;dbname=$dbname", $dbusername, $dbpassword);
$connection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$prepared = $connection->prepare("SELECT COUNT(`username`) FROM `users` WHERE `username` = :bp_username AND `password` = :bp_password ; ");
$prepared->bindParam(':bp_username', $username);
$prepared->bindParam(':bp_password', $password);
$prepared->execute();
if ($prepared->fetchColumn() == 1)
$result=true;
else
$result=false;
}
catch(PDOException $x) { die("Secured"); }
$prepared = null;
$connection = null;
return $result;
}
/*
$dbhost ---> DataBase IP Address
$dbusername ---> DataBase Username
$dbpassword ---> DataBase Password
$dbname ---> DataBase Name
*/
?>
jesse dot chisholm at gmail dot com ¶
4 years ago
@Simon Le Pine
Be aware that:
$search = "user";
$sth = db->prepare("SELECT * FROM users WHERE $search=:email");
and
$search = "email";
$sth = db->prepare("SELECT * FROM users WHERE $search=:email");
will produce two totally different prepared statements.
Doing this _will not work_:
$search = "user";
$sth = db->prepare("SELECT * FROM users WHERE $search=:email");
$sth->execute(array(email=>"yada"));
$search = "email";
$sth->execute(array(email=>"yada@ya.da"));
Kjetil H ¶
6 years ago
Please note that the correct internal method signature is:
<?php public function prepare ($statement, $driver_options = array()) ?>
and NOT:
<?php public function prepare ($statement, array $driver_options = array()) ?>.
Redeclaring the method using the latter method signature throws a Stricts Standards error.
william dot clarke at gmail dot com ¶
12 years ago
Surely if you want to use prepared statements that way you should use the syntax in the second example:
eg.
instead of:
select id,name from demo_de where name LIKE :name OR name=:name
use:
select id,name from demo_de where name LIKE ? OR name=?
I believe you are supposed to either use distinct named parameters (name, name1) OR anonymous parameters (?s)
richard at codevanilla.com ¶
9 years ago
beware
PDO will emulate prepared statements/bound parameters for drivers that do not natively support them, and can also rewrite named or question mark style parameter markers to something more appropriate, if the driver supports one style but not the other.
This includes mySQL it seems so
<?php
try{
$sth1 = $this->db1->prepare($t1, array(PDO::ATTR_CURSOR => PDO::CURSOR_FWDONLY));
}
catch(PDOException $e){
return $this->pack('dbError', $e->getMessage());
}
?>
does not and so will not throw the exception if your SQL is wrong.
You will need to check that $sth1 is not null.
pascal dot buguet at laposte dot net ¶
8 years ago
PDO::CURSOR_SCROLL is ok with MSS.
You must install SQL Server Driver for PHP 2.0 CTP2 : SQLSRV20.EXE
and the native client "Microsoft SQL Server 2008 R2 Native Client" : sqlncli.msi.
sgirard at rossprint dot com ¶
9 years ago
Maybe everyone else already knows this but...
If you have a routine that prepares/executes many insert or update statements for a sqlite db then you may want to make use of the pdo transactions.
On some old hardware my query set went from 12 seconds to 1/3-1/2 second.
-sean
chatelain dot cedric dot pro at gmail dot com ¶
4 years ago
you can't use CREATE DATABASE with prepared statement.
$sql = $conn->prepare("DROP DATABASE IF EXISTS :dbname ;",
array(PDO::ATTR_CURSOR => PDO::CURSOR_FWDONLY));
$sql->execute(array(':dbname' => $dbname));
This will not work.
Anyone has an explanation ?
www.onphp5.com ¶
12 years ago
Please note that the statement regarding driver_options is misleading:
"This array holds one or more key=>value pairs to set attribute values for the PDOStatement object that this method returns. You would most commonly use this to set the PDO::ATTR_CURSOR value to PDO::CURSOR_SCROLL to request a scrollable cursor. Some drivers have driver specific options that may be set at prepare-time"
From this you might think that scrollable cursors work for all databases, but they don't! Check out this bug report:
http://bugs.php.net/bug.php?id=34625
Stan ¶
11 years ago
Using prepared SELECT statements on a MySQL database prior to MySQL 5.1.17 can lead to SERIOUS performance degradation.
Quote from http://dev.mysql.com/doc/refman/5.1/en/query-cache.html :
>> The query cache is not used for server-side prepared statements before MySQL 5.1.17 <<
The MySQL query cache buffers complete query results and is used to satisfy repeated identical queries if the underlying tables do not change in the meantime - just what happens all the time in a typical web application. It speeds up queries by a several hundred to a several thousand percent.
Obviously, it doesn't make much sense to give up query caching for the relatively small performance benefit of prepared statements (i.e. the DBMS not having to parse and optimize the same query multiple times) - so using PDO->query() for SELECT statements is probably the better choice i you're connecting to MySQL < 5.1.17.
