How to apply bindValue method in LIMIT clause?

问题

Here is a snapshot of my code:

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

$fetchPictures->bindValue(\':albumId\', $_GET[\'albumid\'], PDO::PARAM_INT);

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

$fetchPictures->bindValue(\':max\', $max, PDO::PARAM_INT);
$fetchPictures->execute() or die(print_r($fetchPictures->errorInfo()));
$pictures = $fetchPictures->fetchAll(PDO::FETCH_ASSOC);

I get

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near \'\'15\', 15\' at line 1

It seems that PDO is adding single quotes to my variables in the LIMIT part of the SQL code. I looked it up I found this bug which I think is related: http://bugs.php.net/bug.php?id=44639

Is that what I\'m looking at? This bug has been opened since April 2008! What are we supposed to do in the meantime?

I need to build some pagination, and need to make sure the data is clean, sql injection-safe, before sending the sql statement.

回答1:

I remember having this problem before. Cast the value to an integer before passing it to the bind function. I think this solves it.

$fetchPictures->bindValue(':skip', (int) trim($_GET['skip']), PDO::PARAM_INT);

回答2:

The simplest solution would be to switch the emulation mode off. You can do it either as a connection option or simply by adding the following line

$PDO->setAttribute( PDO::ATTR_EMULATE_PREPARES, false );

It will not only solve your problem with bind param, but also let you to send values in execute(), which will make your code muchshorter

$skip = $_GET['skip'] ?: 0;
$sql  = "SELECT * FROM pictures WHERE album = ? ORDER BY id LIMIT ?, ?";
$PDO->setAttribute( PDO::ATTR_EMULATE_PREPARES, false );
$stmt  = $PDO->prepare($sql);
$stmt->execute([$_GET['albumid'], $skip, $max]);
$pictures = $stmt->fetchAll(PDO::FETCH_ASSOC);

回答3:

Looking at the bug report, the following might work:

$fetchPictures->bindValue(':albumId', (int)$_GET['albumid'], PDO::PARAM_INT);

$fetchPictures->bindValue(':skip', (int)trim($_GET['skip']), PDO::PARAM_INT);

but are you sure your incoming data is correct? Because in the error message, there seems to be only one quote after the number (as opposed to the whole number being enclosed in quotes). This could also be an error with your incoming data. Can you do a print_r($_GET); to find out?

回答4:

This just as summary.
There are four options to parameterize LIMIT/OFFSET values:

Disable PDO::ATTR_EMULATE_PREPARES as mentioned above.

Which prevents values passed per ->execute([...]) to always show up as strings.
Switch to manual ->bindValue(..., ..., PDO::PARAM_INT) parameter population.

Which however is less convenient than an ->execute list[].
Simply make an exception here and just interpolate plain integers when preparing the SQL query.
```
 $limit = intval($limit);
 $s = $pdo->prepare("SELECT * FROM tbl LIMIT {$limit}");
```
The casting is important. More commonly you see ->prepare(sprintf("SELECT ... LIMIT %d", $num)) used for such purposes.
If you're not using MySQL, but for example SQLite, or Postgres; you can also cast bound parameters directly in SQL.
```
 SELECT * FROM tbl LIMIT (1 * :limit)
```
Again, MySQL/MariaDB don't support expressions in the LIMIT clause. Not yet.

回答5:

for LIMIT :init, :end

You need to bind that way. if you had something like $req->execute(Array()); it wont work as it will cast PDO::PARAM_STR to all vars in the array and for the LIMIT you absolutely need an Integer. bindValue or BindParam as you want.

$fetchPictures->bindValue(':albumId', (int)$_GET['albumid'], PDO::PARAM_INT);

回答6:

Since nobody has explained why this is happening, I'm adding an answer. The reason it is behaving this was is because you are using trim(). If you look at the PHP manual for trim, the return type is string. You are then trying to pass this as PDO::PARAM_INT. A few ways to get around this are:

Use filter_var($integer, FILTER_VALIDATE_NUMBER_INT) to make sure you are passing an integer.
As others said, using intval()
Casting with (int)
Checking if it is an integer with is_int()

There are plenty more ways, but this is basically the root cause.

回答7:

bindValue offset and limit using PDO::PARAM_INT and it will work

回答8:

//BEFORE (Present error) $query = " .... LIMIT :p1, 30;"; ... $stmt->bindParam(':p1', $limiteInferior);

//AFTER (Error corrected) $query = " .... LIMIT :p1, 30;"; ... $limiteInferior = (int)$limiteInferior; $stmt->bindParam(':p1', $limiteInferior, PDO::PARAM_INT);

回答9:

PDO::ATTR_EMULATE_PREPARES gave me the

Driver does not support this function: This driver doesn't support setting attributes' error.

My workaround was to set a $limit variable as a string, then combine it in the prepare statement as in the following example:

$limit = ' LIMIT ' . $from . ', ' . $max_results;
$stmt = $pdo->prepare( 'SELECT * FROM users WHERE company_id = :cid ORDER BY name ASC' . $limit . ';' );
try {
    $stmt->execute( array( ':cid' => $company_id ) );
    ...
}
catch ( Exception $e ) {
    ...
}

来源：https://stackoverflow.com/questions/2269840/how-to-apply-bindvalue-method-in-limit-clause

标签

php

mysql

sql

pdo

bindvalue