getting single cell from database using PDO - php

Question

I am trying to get a piece of data from my database but would like to only get one cell using the PDO statement if this is possible.
Below is a screenshot of the table
The table name is called heating
I am trying to get the data from column called 'garage' and row id = 3
I have tried many ways but keep failing. The following is what I have so far but only returns the column name garage for some reason.
I am using the following which gives me the name garage
$room = 'garage';
require_once "connect.php";
$sql = 'SELECT :name FROM heating WHERE id = 3';
$stmt = $pdo->prepare($sql);
$stmt->bindParam(':name', $room);
$stmt->execute();
$sw = $stmt->fetch();
echo $sw[0];
If I do the following I gives me the correct outcome but I would like to replace garage with a variable
$sql = 'SELECT garage FROM heating WHERE id = 3';
$stmt = $pdo->prepare($sql);
$stmt->execute();
$sw = $stmt->fetch();
echo $sw[0];

Answer 1

You can create a white list of your column names and use it to select the right column. You can check the column against a white list with the help of in_array. The third parameter is very important as it checks that string is a string. You can only then safely concatenate the SQL with your PHP variables using PHP concatenation operator. For the good measure, the column names should be enclosed in backticks `, in case any of your column names is a reserved word or contains special characters.
$whiteListOfHeating = [
'keyName',
'den',
'WC1',
'hallway',
'garage'
];
$room = 'garage';
if (in_array($room, $whiteListOfHeating, true)) {
$sql = 'SELECT `'.$room.'` FROM heating WHERE id = 3';
$stmt = $pdo->prepare($sql);
// ...
} else {
echo 'Invalid column name specified!';
}

Answer 2

Sometimes simplest solutions are best.
require_once "connect.php";
$room = 'garage';
$sql = 'SELECT * FROM heating WHERE id = ?';
$stmt = $pdo->prepare($sql);
$stmt->execute([3]);
$sw = $stmt->fetch();
echo $sw[$room];
Besides, every time you need such a functionality, in means that most likely your database structure is wrong. A room should be a row, not column
require_once "connect.php";
$room = 'garage';
$sql = 'SELECT value FROM heating_room WHERE heating_id=3 and room = ?';
$stmt = $pdo->prepare($sql);
$stmt->execute([$room]);
$sw = $stmt->fetchColumn();
echo $sw;
will make it straight