What role does the SQL expression play in causing errors like "Invalid parameter number" in PHP scripts?

The "Invalid parameter number" error in PHP scripts occurs when the number of placeholders in the SQL query does not match the number of parameters passed to the query. To solve this issue, ensure that the number of placeholders in the SQL query matches the number of parameters being bound to the query. 

// Example of fixing "Invalid parameter number" error
$stmt = $pdo->prepare("SELECT * FROM users WHERE username = :username AND email = :email");
$stmt->bindParam(':username', $username);
$stmt->bindParam(':email', $email);
$stmt->execute();

Keywords

SQL expression errors Invalid parameter number PHP scripts

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