In database management systems (DBMS), a prepared statement, parameterized statement, or parameterized query is a feature where the database pre-compiles SQL code and stores the results, separating it from data. Benefits of prepared statements are:^[1]

• efficiency, because they can be used repeatedly without re-compiling
• security, by reducing or eliminating SQL injection attacks

A prepared statement takes the form of a pre-compiled template into which constant values are substituted during each execution, and typically use SQL DML statements such as INSERT, SELECT, or UPDATE.

A common workflow for prepared statements is:

1. Prepare: The application creates the statement template and sends it to the DBMS. Certain values are left unspecified, called parameters, placeholders or bind variables (labelled "?" below):

   INSERT INTO products (name, price) VALUES (?, ?);

2. Compile: The DBMS compiles (parses, optimizes and translates) the statement template, and stores the result without executing it.
3. Execute: The application supplies (or binds) values for the parameters of the statement template, and the DBMS executes the statement (possibly returning a result). The application may request the DBMS to execute the statement many times with different values. In the above example, the application might supply the values "bike" for the first parameter and "10900" for the second parameter, and then later the values "shoes" and "7400".

The alternative to a prepared statement is calling SQL directly from the application source code in a way that combines code and data. The direct equivalent to the above example is:

INSERT INTO products (name, price) VALUES ('bike', '10900');

Not all optimization can be performed at the time the statement template is compiled, for two reasons: the best plan may depend on the specific values of the parameters, and the best plan may change as tables and indexes change over time.^[2]

On the other hand, if a query is executed only once, server-side prepared statements can be slower because of the additional round-trip to the server.^[3] Implementation limitations may also lead to performance penalties; for example, some versions of MySQL did not cache results of prepared queries.^[4] A stored procedure, which is also precompiled and stored on the server for later execution, has similar advantages. Unlike a stored procedure, a prepared statement is not normally written in a procedural language and cannot use or modify variables or use control flow structures, relying instead on the declarative database query language. Due to their simplicity and client-side emulation, prepared statements are more portable across vendors.

Software support

Major DBMSs, including SQLite,^[5] MySQL,^[6] Oracle,^[7] IBM Db2,^[8] Microsoft SQL Server^[9] and PostgreSQL^[10] support prepared statements. Prepared statements are normally executed through a non-SQL binary protocol for efficiency and protection from SQL injection, but with some DBMSs such as MySQL prepared statements are also available using a SQL syntax for debugging purposes.^[11]

A number of programming languages support prepared statements in their standard libraries and will emulate them on the client side even if the underlying DBMS does not support them, including Java's JDBC,^[12] Perl's DBI,^[13] PHP's PDO^[1] and Python's DB-API.^[14] Client-side emulation can be faster for queries which are executed only once, by reducing the number of round trips to the server, but is usually slower for queries executed many times. It resists SQL injection attacks equally effectively.

Many types of SQL injection attacks can be eliminated by disabling literals, effectively requiring the use of prepared statements; as of 2007 only H2 supports this feature.^[15]

Examples

import com.mysql.jdbc.jdbc2.optional.MysqlDataSource;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class Main {

    public static void main(String[] args) throws SQLException {
        MysqlDataSource ds = new MysqlDataSource();
        ds.setDatabaseName("mysql");
        ds.setUser("root");

        try (Connection conn = ds.getConnection()) {
            try (Statement stmt = conn.createStatement()) {
                stmt.executeUpdate("CREATE TABLE IF NOT EXISTS products (name VARCHAR(40), price INT)");
            }

            try (PreparedStatement stmt = conn.prepareStatement("INSERT INTO products VALUES (?, ?)")) {
                stmt.setString(1, "bike");
                stmt.setInt(2, 10900);
                stmt.executeUpdate();
                stmt.setString(1, "shoes");
                stmt.setInt(2, 7400);
                stmt.executeUpdate();
                stmt.setString(1, "phone");
                stmt.setInt(2, 29500);
                stmt.executeUpdate();
            }

            try (PreparedStatement stmt = conn.prepareStatement("SELECT * FROM products WHERE name = ?")) {
                stmt.setString(1, "shoes");
                ResultSet rs = stmt.executeQuery();
                rs.next();
                System.out.println(rs.getInt(2));
            }
        }
    }
}

<?php

try {
    // Connect to a database named "mysql", with the password "root"
    $connection = new PDO('mysql:dbname=mysql', 'root');

    // Execute a request on the connection, which will create
    // a table "products" with two columns, "name" and "price"
    $connection->exec('CREATE TABLE IF NOT EXISTS products (name VARCHAR(40), price INT)');

    // Prepare a query to insert multiple products into the table
    $statement = $connection->prepare('INSERT INTO products VALUES (?, ?)');
    $products  = [
        ['bike', 10900],
        ['shoes', 7400],
        ['phone', 29500],
    ];

    // Iterate through the products in the "products" array, and
    // execute the prepared statement for each product
    foreach ($products as $product) {
        $statement->execute($product);
    }

    // Prepare a new statement with a named parameter
    $statement = $connection->prepare('SELECT * FROM products WHERE name = :name');
    $statement->execute([
        ':name' => 'shoes',
    ]);

    // Use array destructuring to assign the product name and its price
    // to corresponding variables
    [ $product, $price ] = $statement->fetch();

    // Display the result to the user
    echo "The price of the product {$product} is \${$price}.";

    // Close the cursor so `fetch` can eventually be used again
    $statement->closeCursor();
} catch (\Exception $e) {
    echo 'An error has occurred: ' . $e->getMessage();
}

#!/usr/bin/perl -w
use strict;
use DBI;

my ($db_name, $db_user, $db_password) = ('my_database', 'moi', 'Passw0rD');
my $dbh = DBI->connect("DBI:mysql:database=$db_name", $db_user, $db_password,
    { RaiseError => 1, AutoCommit => 1})
    or die "ERROR (main:DBI->connect) while connecting to database $db_name: " .
        $DBI::errstr . "\n";

$dbh->do('CREATE TABLE IF NOT EXISTS products (name VARCHAR(40), price INT)');

my $sth = $dbh->prepare('INSERT INTO products VALUES (?, ?)');
$sth->execute(@$_) foreach ['bike', 10900], ['shoes', 7400], ['phone', 29500];

$sth = $dbh->prepare("SELECT * FROM products WHERE name = ?");
$sth->execute('shoes');
print "$$_[1]\n" foreach $sth->fetchrow_arrayref;
$sth->finish;

$dbh->disconnect;

using (SqlCommand command = connection.CreateCommand())
{
    command.CommandText = "SELECT * FROM users WHERE USERNAME = @username AND ROOM = @room";
    command.Parameters.AddWithValue("@username", username);
    command.Parameters.AddWithValue("@room", room);

    using (SqlDataReader dataReader = command.ExecuteReader())
    {
        // ...
    }
}

import mysql.connector

with mysql.connector.connect(database="mysql", user="root") as conn:
    with conn.cursor(prepared=True) as cursor:
        cursor.execute("CREATE TABLE IF NOT EXISTS products (name VARCHAR(40), price INT)")
        params = [("bike", 10900),
                  ("shoes", 7400),
                  ("phone", 29500)]
        cursor.executemany("INSERT INTO products VALUES (%s, %s)", params)
        params = ("shoes",)
        cursor.execute("SELECT * FROM products WHERE name = %s", params)
        print(cursor.fetchall()[0][1])

Virtual username  Alpha 20   init: 'sister'
Virtual password  Alpha 20   init: 'yellow'

SQL Command:   SELECT * FROM users WHERE USERNAME=:1 AND PASSWORD=:2

Input Arguments: 
1:  username
2:  password

SetDatabaseBlob, SetDatabaseDouble, SetDatabaseFloat, SetDatabaseLong, SetDatabaseNull, SetDatabaseQuad, SetDatabaseString

SetDatabaseString(#Database, 0, "test")  
If DatabaseQuery(#Database, "SELECT * FROM employee WHERE id=?")    
  ; ...
EndIf

SetDatabaseString(#Database, 0, "Smith") ; -> $1 
SetDatabaseString(#Database, 1, "Yes")   ; -> $2
SetDatabaseLong  (#Database, 2, 50)      ; -> $3

If DatabaseQuery(#Database, "SELECT * FROM employee WHERE id=$1 AND active=$2 AND years>$3")    
  ; ...
EndIf

See also

• Code injection

References