Using PDO::quote to Safely Quote Strings in PHP

When building SQL statements in PHP, strings often need to be quoted to avoid syntax errors or injection vulnerabilities. The built‑in PDO::quote() method can automatically add appropriate quotes and escape characters.

Syntax of the method is:

<code>public PDO::quote(string $string, int $parameter_type = PDO::PARAM_STR) : string</code>

$string : the string that needs quoting.

$parameter_type : optional driver‑specific hint for the data type, defaulting to PDO::PARAM_STR .

The method returns the quoted string, which can be safely embedded in an SQL query. If the driver does not support quoting, false is returned.

Example 1 – Quoting a normal string

<code>&lt;?php
$servername = "localhost";
$username = "root";
$password = "root123456";
$dbname   = "my_database";

try {
    $pdo = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    echo "连接成功" . "<br>";
    // $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $pdo->setAttribute(PDO::ATTR_CASE, PDO::CASE_UPPER);
    $string = 'Nice';
    print "Unquoted string: $string";
    echo "<br>";
    print "Quoted string: " . $pdo->quote($string) . "\n";
} catch (PDOException $e) {
    echo $e->getMessage();
}
// Output:
// 连接成功
// Unquoted string: Nice
// Quoted string: 'Nice'
?></code>

Example 2 – Quoting a potentially dangerous string

<code>&lt;?php
$servername = "localhost";
$username = "root";
$password = "root123456";
$dbname   = "my_database";

try {
    $pdo = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    echo "连接成功" . "<br>";
    // $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $pdo->setAttribute(PDO::ATTR_CASE, PDO::CASE_UPPER);
    $string = 'Naughty \' string';
    print "Unquoted string: $string";
    echo "<br>";
    print "Quoted string:" . $pdo->quote($string);
} catch (PDOException $e) {
    echo $e->getMessage();
}
// Output:
// 连接成功
// Unquoted string: Naughty ' string
// Quoted string:'Naughty \' string'
?></code>

These examples demonstrate how PDO::quote() can be used to safely prepare strings for inclusion in SQL statements, handling both ordinary and special characters.