变量调用在sql语句中不起作用[duplicate]

Question

This question already has an answer here:

• What is the difference between single-quoted and double-quoted strings in PHP? 10 answers

if i put

$sql1 = 'Select * from follow WHERE followmak = $usid';

it does not work

and whenever I put

$sql1 = 'Select * from follow WHERE followmak = 1';

1 or any cardinal number it works out. I tries to echo $usid and it works and but I wonder why it does not work in sql statement , please help me I am noob in PHP

My Full Code is given below :

try {

    $pdo = new PDO("mysql:host=$host;dbname=$dbname", $username, $password);

 $sql = 'SELECT * from follow';


$q = $pdo->query($sql);

$q->setFetchMode(PDO::FETCH_ASSOC);
 $usid = ($row7['userID']);
 $sql1 = 'Select * from follow WHERE followmak = $usid';



 $q1 = $pdo->prepare($sql1);
$q1->execute([$usid]);
$q1->setFetchMode(PDO::FETCH_ASSOC);


} catch (PDOException $e) {

    die("Could not connect to the database $dbname :" . $e->getMessage());

}

?> 

Answer 1

Try using double quote,

$sql1 = "Select * from follow WHERE followmak = $usid";

There's a difference between using single quot (') and double quot ("). using single quot, php will interpret it as string while using double quot php will display the value of the variable into a string.