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Prepared statementIn 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]
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:
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 supportMajor 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[update] only H2 supports this feature.[15] ExamplesGo// Define a BookModel type which wraps a sql.DB connection pool.
type BookModel struct {
DB *sql.DB
}
// This will insert a new book into the database.
func (m *BookModel) Insert(title, author string) (int, error) {
stmt := "INSERT INTO book (title, author, created) VALUES(?, ?, UTC_TIMESTAMP())"
result, err := m.DB.Exec(stmt, title, author)
if err != nil {
return 0, err
}
id, err := result.LastInsertId() // Not support in postgress driver
if err != nil {
return 0, err
}
// The ID returned has the type int64, so we convert it to an int type
// before returning.
return int(id), nil
}
The placeholder parameter syntax differs depending on your database. MySQL, SQL Server and SQLite use the ? notation, but PostgreSQL uses the $N notation. For example, if you were using PostgreSQL instead you would write: _, err := m.DB.Exec("INSERT INTO ... VALUES ($1, $2, $3)", ...)
Java JDBCThis example uses Java and JDBC: 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));
}
}
}
}
Java PHP PDOThis example uses PHP and PDO[16]: <?php
// Connect to a database named "mysql", with the password "root"
$connection = new PDO('mysql:host=127.0.0.1;dbname=test;charset=utf8mb4', '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 \${$price}.";
Perl DBIThis example uses Perl and DBI: #!/usr/bin/perl -w
use strict;
use DBI;
my ($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;
C# ADO.NETThis example uses C# and ADO.NET: 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())
{
// ...
}
}
ADO.NET However, the AddWithValue method should not be used with variable length data types, like varchar and nvarchar. This is because .NET assumes the length of the parameter to be the length of the given value, rather than getting the actual length from the database via reflection. The consequence of this is that a different query plan is compiled and stored for each different length. In general, the maximum number of "duplicate" plans is the product of the lengths of the variable length columns as specified in the database. For this reason, it is important to use the standard Add method for variable length columns:
Since the standard Add method needs to be used for variable length data types, it is a good habit to use it for all parameter types. Python DB-APIThis example uses Python and DB-API: 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])
Magic Direct SQLThis example uses Direct SQL from Fourth generation language like eDeveloper, uniPaaS and magic XPA from Magic Software Enterprises Virtual username Alpha 20 init: 'sister'
Virtual password Alpha 20 init: 'yellow'
SQL Command:
PureBasicPureBasic (since v5.40 LTS) can manage 7 types of link with the following commands SetDatabaseBlob, SetDatabaseDouble, SetDatabaseFloat, SetDatabaseLong, SetDatabaseNull, SetDatabaseQuad, SetDatabaseString There are 2 different methods depending on the type of database For SQLite, ODBC, MariaDB/Mysql use: ? SetDatabaseString(#Database, 0, "test")
If DatabaseQuery(#Database, "SELECT * FROM employee WHERE id=?")
; ...
EndIf
For PostgreSQL use: $1, $2, $3, ... 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 alsoReferences
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