How to Correctly Use Bind Variables in a SQL LIMIT Clause?

Correctly use bind variables in the SQL LIMIT clause

Question:

When trying to use bindValue to set the skip and max values ​​of the LIMIT clause, the generated SQL statement is invalid because single quotes are added to the variables. How to solve this problem?

Answer:

To solve this problem, cast the variable value to an integer before passing it to the bindValue function. This ensures that single quotes are not added, thus resolving SQL syntax errors.

The following is the modified code:

$fetchPictures = $PDO->prepare("SELECT * 
    FROM pictures 
    WHERE album = :albumId 
    ORDER BY id ASC 
    LIMIT :skip, :max");

$fetchPictures->bindValue(':albumId', (int)$_GET['albumid'], PDO::PARAM_INT); // 强制转换为整数

if(isset($_GET['skip'])) {
    $fetchPictures->bindValue(':skip', (int) trim($_GET['skip']), PDO::PARAM_INT);    
} else {
    $fetchPictures->bindValue(':skip', 0, PDO::PARAM_INT);  
}

$fetchPictures->bindValue(':max', (int)$max, PDO::PARAM_INT); // 强制转换为整数
$fetchPictures->execute() or die(print_r($fetchPictures->errorInfo()));
$pictures = $fetchPictures->fetchAll(PDO::FETCH_ASSOC);

The key is to explicitly convert the $_GET['albumid'] and $max variables to an integer type before bindValue. This avoids PDO treating them as strings and adding single quotes, causing syntax errors in the LIMIT clause. The trim() function is used to remove any extra spaces in the $_GET['skip'] variable.

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