Select returning empty query - php

Question

I'm trying to select data where by acc_id
What I get in my localhost: []
However, when I set a specific acc_id i get the correct row is there something in my syntax?
<?php
header('Access-Control-Allow-Origin: *');
// Define database connection parameters
$hn = 'localhost';
$un = 'root';
$pwd = '';
$db = 'ringabell';
$cs = 'utf8';
// Set up the PDO parameters
$dsn = "mysql:host=" . $hn . ";port=3306;dbname=" . $db . ";charset=" . $cs;
$opt = array(
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_OBJ,
PDO::ATTR_EMULATE_PREPARES => false,
);
// Create a PDO instance (connect to the database)
$pdo = new PDO($dsn, $un, $pwd, $opt);
$data = array();
// Attempt to query database table and retrieve data
try {
$acc_id = $pdo->prepare('SELECT acc_id FROM account_info');
$stmt = $pdo->prepare('SELECT p_fname, p_lname, p_condition FROM patient_info WHERE acc_id = "$acc_id"');
$stmt->execute([$acc_id]);
while($row = $stmt->fetch(PDO::FETCH_ASSOC))
{
// Assign each row of data to associative array
$data[] = $row;
}
// Return data as JSON
echo json_encode($data);
}
catch(PDOException $e)
{
echo $e->getMessage();
}
?>

Answer 1

It seems like you want to use the prepared statement but instead executing your query instantly. If you want to bind the value to your query use something like this:
$acc_id = // get the $acc_id value from somewhere you want
$stmt = $pdo->prepare('SELECT p_fname, p_lname, p_condition FROM patient_info WHERE acc_id = ?');
$stmt->execute([$acc_id]);
while($row = $stmt->fetch(PDO::FETCH_ASSOC))
{
// Assign each row of data to associative array
$data[] = $row;
}
Example with using a placeholder
Instead of executing your statement with the array of params, you could also use the bindValue() or the bindParam() method:
$stmt = $pdo->prepare('SELECT p_fname, p_lname, p_condition FROM patient_info WHERE acc_id = :acc_id');
$stmt->bindValue(':acc_id', $acc_id);
$stmt->execute();
// everything else works as previous
The difference between these two methods is written in docs:
bindValue():
Binds a value to a corresponding named or question mark placeholder in the SQL statement that was used to prepare the statement.
bindParam():
Binds a PHP variable to a corresponding named or question mark placeholder in the SQL statement that was used to prepare the statement. Unlike PDOStatement::bindValue(), the variable is bound as a reference and will only be evaluated at the time that PDOStatement::execute() is called.