Learn how to use PDO prepared statements

PDO is a method of accessing databases in PHP. It can interact with different relational databases. PDO prepared statements are a feature that makes PDO more powerful, and it can effectively avoid security issues such as SQL injection.

This article will introduce PDO prepared statements, focusing on how to use PDO prepared statements for database operations.

What is a PDO prepared statement?

PDO prepared statement is a method of preparing SQL statements first and then executing them. It prevents SQL injection attacks by dividing the SQL query statement into two steps, the first step is to prepare the query, and the second step is to execute the query.

Advantages of using PDO prepared statements:

1. Security check

Using PDO prepared statements can prevent SQL injection attacks. When preparing queries, statements similar to this: $stmt = $pdo->prepare("SELECT * FROM users WHERE username = :username AND password = :password");, they use colons (:) to define parameters, and Parameter separation and escaping of SQL statements.

2. Performance improvement

Every time a PDO prepared statement is called, the database only needs to be compiled and optimized once instead of executing the query every time, which can improve query efficiency.

3. Data type prompt

PDO prepared statements can provide data type prompts to ensure that the parameters received by the database are correct. For example, PDO::PARAM_INT can be used for integer types.

How to use PDO prepared statements

Before using PDO prepared statements, you need to connect to the database. Here is a code example for connecting to a MySQL database:

<?php
$dsn = 'mysql:host=localhost;dbname=test';
$username = 'root';
$password = '';

try {
    $pdo = new PDO($dsn, $username, $password);
} catch (PDOException $e) {
    echo 'Connection failed: ' . $e->getMessage();
    exit;
}

Now that we have connected to the database, we can start using PDO prepared statements. Suppose we have a users table, which contains the following fields: id, username and password.

First, we need to prepare a query statement. For example, if we want to get users whose usernames and passwords match, we can define a prepared statement as follows:

$stmt = $pdo->prepare("SELECT * FROM users WHERE username = :username AND password = :password");

Use colons (:) here to define the variables we want to query, ":username" and ":password" "They are all variables.

Next, we need to bind values ​​to these variables. This can be done through the bindParam() or bindValue() method. bindParam() is more versatile, it can be used multiple times during the lifetime of the variable.

$stmt->bindParam(':username', $username);
$stmt->bindParam(':password', $password);

The purpose of bindValue() is to bind the value to the variable once. If our variable does not need to be used anymore, it is recommended to use this method:

$stmt->bindValue(':username', $username);
$stmt->bindValue(':password', $password);

Here, $username and $password is the username and password we want to query.

Finally, we need to execute the query:

$stmt->execute();

while ($row = $stmt->fetch()) {
    // do something with the rows
}

The fetch() method fetches the query results in rows and returns each row as an array. We can use this result set in a loop, operating on each row.

Summary

PDO prepared statements are one of the most effective ways to avoid SQL injection. When preparing a query, colons are used to specify parameters, separate parameters, and escape SQL statements. Each time a PDO prepared statement is called, the database only needs to compile and optimize one query instead of optimizing every query, which can improve query efficiency.

In this article, we introduce how to use PDO prepared statements and related methods. This would be a very useful tip to use in higher level applications or when preventing SQL injection attacks.

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