What do these signs?

$sql = "INSERT INTO catalog (title, author, pubyear, price)
VALUES (?,?,?,?)";
Who can tell what the question marks in brackets value? What do they mean and why?
September 19th 19 at 13:26
2 answers
September 19th 19 at 13:28
September 19th 19 at 13:30
This substitution of values, the first '?' is set to 'title' and so on. Protection from SQL injection.
Look in the direction of PDO.

Find more questions by tags MySQLPHP