I have the following code:
public function getDefinitions($wordID) {
$query = $this->dbc->prepare('SELECT * FROM definitions WHERE wordID = ?');
$query->bind_param('i', $wordID);
$query->execute();
// ...
$query->close();
return $result;
}
It would seem that this would recreate the prepared statement for each invocation. That does not seem to take advantage of the full benefit of prepared statements. Especially in the case these prepare statements were stored server side. Is that true?
If so, should I store the prepare statement (in this case as a property) to persist it between invocations. Is there a way to persist the prepared statement between requests? I assume that's essentially a stored procedure?
Currently I am using MySQLi. Please note any API difference if I were using another driver (e.g. PDO).
should I store the prepare statement (in this case as a property) to persist it between invocations.
I wouldn't say you "should". You may, if you foresee a lot of consequent invocations (which you cannot group up to call at once). Either way, you scarcely will be able to notice the real life difference.
Is there a way to persist the prepared statement between requests?
In PHP - no. Prepared statements are connection-based, connection is closed along with request, and persistent connections won't help you either, as mysqli is using designated mechanism to clean connection state before reuse.
Please note any API difference if I were using another driver (e.g. PDO).
PDO has an advantage over mysqli as it can emulate prepared statements, eliminating even such a negligible overhead of two database calls, which makes it more suitable for the real life usage (beside other key benefits).
In a nutshell, the "prepare once-multiple execute" feature of native prepared statements can have noticeable effect only for a huge number of queries, starting from thousands.
You should persist the query if you plan on using it again.
As you are using mysqli prepared statements should always be real prepared statements. (In contradiction to PDO, which emulates queries based on the used driver and might not send an additional database call). The data replacing the placeholders is then sent in a different pack of data.
A nativly-prepared statement takes therefore two trips to the database if only issued once.
Sending this extra action takes time. If you know that you only want to issue the query once, it might in certain circumstances be positive to use traditional queries. (However, this can only be advisable if you are absolutly sure about the potential negative security implications standard queries have in comparison to prepared statements. The added level safety using prepared statements outwights the benefit such a change may have in most cases.)
However, if you want to re-run the query preparing it is the right approach. MySQL is supposed to cache converted statements, so the php-site is the only way of optimizing and reusing.
What you can do is to prevent the additional call to the prepare method and the action it may trigger in the low-level database connector by preserving the statement in the method using a static variable or a property. The impact on most real applications is however arguable.
Related
I've used the following sort of code a few times in my current project to clear out some tables. Incase it's not obvious I'm using PDO.
$clearResult = $db->query('TRUNCATE TABLE table_name');
I'm currently going through and updating a few of my earlier scripts to make sure they all make use of prepared statements and are written in a way to reduce (hopefully stop) sql injection.
No, there's no user input in the actual query so there's no risk of injection.
You do have to make sure that a user isn't able to trigger the truncate though, unless they're authorized.
It's not the SQL operation that determines whether or not a prepared statement should be used. To prevent SQL Injection, a prepared statement should be used when any variable is involved in the query where bound parameters are permitted. That is not limited to just user input either, any variable at all should be a bound paremeter, regardless of where it came from.
In your example there are no variables required for the query, and so there is no security benefit of using a prepared statement.
Even if your table_name was coming from user input or a variable, a prepared statement would not be a solution because it is not possible to bind the table name.
Prepared statements would have no effect on your truncate query.
PDO prepared statements are useful when running queries with user input as they allow you to use features such as bound parameters to sanitise user input.
They are also useful for optimising queries that will run multiple times.
You might want to read up a little on prepared statements in the PHP documentation - PHP documentation for prepared statements:
Many of the more mature databases support the concept of prepared
statements. What are they? They can be thought of as a kind of
compiled template for the SQL that an application wants to run, that
can be customized using variable parameters. Prepared statements offer
two major benefits:
The query only needs to be parsed (or prepared) once, but can be
executed multiple times with the same or different parameters. When
the query is prepared, the database will analyze, compile and optimize
its plan for executing the query. For complex queries this process can
take up enough time that it will noticeably slow down an application
if there is a need to repeat the same query many times with different
parameters. By using a prepared statement the application avoids
repeating the analyze/compile/optimize cycle. This means that prepared
statements use fewer resources and thus run faster.
The parameters to
prepared statements don't need to be quoted; the driver automatically
handles this. If an application exclusively uses prepared statements,
the developer can be sure that no SQL injection will occur (however,
if other portions of the query are being built up with unescaped
input, SQL injection is still possible). Prepared statements are so
useful that they are the only feature that PDO will emulate for
drivers that don't support them. This ensures that an application will
be able to use the same data access paradigm regardless of the
capabilities of the database.
I'm re-engineering a PHP-driven web site which uses a minimal database. The original version used "pseudo-prepared-statements" (PHP functions which did quoting and parameter replacement) to prevent injection attacks and to separate database logic from page logic.
It seemed natural to replace these ad-hoc functions with an object which uses PDO and real prepared statements, but after doing my reading on them, I'm not so sure. PDO still seems like a great idea, but one of the primary selling points of prepared statements is being able to reuse them… which I never will. Here's my setup:
The statements are all trivially simple. Most are in the form SELECT foo,bar FROM baz WHERE quux = ? ORDER BY bar LIMIT 1. The most complex statement in the lot is simply three such selects joined together with UNION ALLs.
Each page hit executes at most one statement and executes it only once.
I'm in a hosted environment and therefore leery of slamming their servers by doing any "stress tests" personally.
Given that using prepared statements will, at minimum, double the number of database round-trips I'm making, am I better off avoiding them? Can I use PDO::MYSQL_ATTR_DIRECT_QUERY to avoid the overhead of multiple database trips while retaining the benefit of parametrization and injection defense? Or do the binary calls used by the prepared statement API perform well enough compared to executing non-prepared queries that I shouldn't worry about it?
EDIT:
Thanks for all the good advice, folks. This is one where I wish I could mark more than one answer as "accepted" — lots of different perspectives. Ultimately, though, I have to give rick his due… without his answer I would have blissfully gone off and done the completely Wrong Thing even after following everyone's advice. :-)
Emulated prepared statements it is!
Today's rule of software engineering: if it isn't going to do anything for you, don't use it.
I think you want PDO::ATTR_EMULATE_PREPARES. That turns off native database prepared statements, but still allows query bindings to prevent sql injection and keep your sql tidy. From what I understand, PDO::MYSQL_ATTR_DIRECT_QUERY turns off query bindings completely.
When not to use prepared statements? When you're only going to be running the statement once before the db connection goes away.
When not to use bound query parameters (which is really what most people use prepared statements to get)? I'm inclined to say "never" and I'd really like to say "never", but the reality is that most databases and some db abstraction layers have certain circumstances under which they won't allow you to bind parameters, so you're forced to not use them in those cases. Any other time, though, it will make your life simpler and your code more secure to use them.
I'm not familiar with PDO, but I'd bet it provides a mechanism for running parametrized queries with the values given in the same function call if you don't want to prepare, then run as a separate step. (e.g., Something like run_query("SELECT * FROM users WHERE id = ?", 1) or similar.)
Also, if you look under the hood, most db abstraction layers will prepare the query, then run it, even if you just tell it to execute a static SQL statement. So you're probably not saving a trip to the db by avoiding explicit prepares anyhow.
Prepared statements are being used by thousands of people and are therefore well-tested (and thus one can infer they are reasonably secure). Your custom solution is only used by you.
The chance that your custom solution is insecure is pretty high. Use prepared statements. You have to maintain less code that way.
The benefits of prepared statements are as follows:
each query is only compiled once
mysql will use a more efficient transport format to send data to the server
However, prepared statements only persist per connection. Unless you're using connection pooling, there would be no benefit if you're only doing one statement per page. Trivially simple queries would not benefit from the more efficient transport format, either.
Personally I wouldn't bother. The pseudo-prepared statements are likely to be useful for the safe variable quoting they presumably provide.
Honestly, I don't think you should worry about it. However, I remember that a number of PHP data access frameworks supported prepare statement modes and non-prepare statement modes. If I remember correctly, PEAR:DB did back in the day.
I have ran into the same issue as you and I had my own reservations, so instead of using PDO I ended up writing my own light-weight database layer that supported prepares and standard statements and performed correct escaping (sql-injection prevention) in both cases. One of my other gripes with prepares is that sometimes it is more efficient to append some non-escapable input to a statement like ... WHERE id IN (1, 2, 3...).
I don't know enough about PDO to tell you what other options you have using it. However, I do know that PHP has escaping functions available for all database vendors it supports and you could roll your own little layer on top of any data access layer you are stuck with.
I am thinking of rewriting some open-source application for my purposes to PDO and transactions using InnoDB (mysql_query and MyISAM now).
My question is: Which cases are reasonable for using prepared statements?
Because everywhere I am reading is stated (even in many posts here) that I should use prepared statements every time and everywhere because of the 1. security and 2. performance. Even PHP manual recommends using prepared statements and not mentioning the escape-thing.
You can't deny the security mechanism. But thinking it over and over it comes to mind that having to prepare the statement every time and then use it once.. It doesn't make sense. While having to insert 1000 times some variables in single statement, that makes sense but it is obvious. But this is not what common eshop or board is built upon.
So how to overcome this? May I prepare my statements application-wide and to name them specifically? Can I prepare several different statements and to use them by name? Because this is the only reasonable solution I am thinking of (except the 1000x thing).
I found there is this mysql_real_escape called $pdo->quote as well for the purpose of single query. Why not to use this? Why to bother with preparing?
And what do you think of this excellent article?
http://blog.ulf-wendel.de/2008/pdo_mysqlnd-prepared-statements-again/
Do you agree with the overhead caused by preparing the statements?
Thanks
I think this falls in the "premature optimization" category.
How significant is the overhead? Have you measured it? Does it affect your server performance at all?
Odds are it doesn't.
On the plus side, you have an undeniable gain in terms of security (which should be a major concern for any internet-based shop).
On the downside, you have the risk that it might affect performance. In the link you provided, it shows that poorly implemented PDO preparation results in slightly lower performance than non prepared statement in some circumstances. Performance difference on 5000 runs is 0.298 seconds.
Insignificant. Even more so when you realize that the "non prepared" queries are run without the input sanitizing routines that would be required to make them safe in a live environment. If you don't use the prepared queries, you need some form of input sanitizing to prevent SQL attacks, and depending on how it is done, you may need to massage back the result sets.
Bottom line, there is no significant performance issue, but there is a significant security benefit. Thus the official recommendation of using prepared statements.
In your question, you speak of "the common eshop". The "common eshop" will never have enough traffic to worry about the performance issue, if there is one. The security issue on the other end...
My question is: Which cases are reasonable for using prepared statements?
All of them. The community is openly-opposed to the usage of mysql_* functions.
Note: Suggested alternatives
Use of this extension is discouraged. Instead, the MySQLi or PDO_MySQL extension should be used. See also MySQL: choosing an API for more information.
Alternatives to this function include:
mysqli_connect()
PDO::__construct()
source
But thinking it over and over it comes to mind that having to prepare the statement every time and then use it once.. It doesn't make sense
You're trading in a Geo for a Jaguar and you're complaining that you don't like the Jaguar because you don't always use the seat-heaters. You don't have to be consistently using every function of a library to mean it's good.
I found there is this mysql_real_escape called $pdo->quote as well for the purpose of single query. Why not to use this? Why to bother with preparing?
If you are using this function to build SQL statements, you are strongly recommended to use PDO::prepare() to prepare SQL statements with bound parameters instead of using PDO::quote() to interpolate user input into an SQL statement. Prepared statements with bound parameters are not only more portable, more convenient, immune to SQL injection, but are often much faster to execute than interpolated queries, as both the server and client side can cache a compiled form of the query. source
My question is: Which cases are reasonable for using prepared statements?
Well actually, that's hard to say. Especially as you didn't even tell which open source application you speak about here.
To give you an example: For a ultra-lame guestbook app PDO with prepared statements will be the perfect choice, as well for 99% of all other open source apps out there. But for some this actually can make a difference. The important part here is: You have not told anything about the application.
As the database is not unimportant to an application, it's the other way round as well: the application is not unimportant to the database.
So you either need to share more about that "mysterious" open-source application you ask about or you need to tell us, what exactly you would like to know. Because generally, it's simple: Take PDO. But in specific, there are differences, so you need to tell us what the application in specific is, otherwise your question is already answered.
And btw., if the application is mysql_* style, it's much easier to just replace with mysqli_* interface. If you had done some actually rewriting, even just for fun, you would have seen that.
So better add more meat here or live with some not-so-precise answers.
While this question is rather old, some topics were not really discussed that should be outlined here for others researching the same as the OP.
To summarize everything below:
Yes always use prepare statements
Yes use PDO over mysqli over mysql. This way if you switch database systems all you need to do is update the queries instead of queries, function calls, and arguments given it supports prepared statements.
Always sanitize user supplied data despite using prepared statements with parameters
Look into a DBAL (Database Abstraction Layer) to ease working with all of these factors and manipulating queries to suit your needs.
There is the topic of PDO::ATTR_EMULATE_PREPARES which will increase the performance of calling cached queries in MySQL >= 5.1.21 when emulation is turned OFF, which is ENABLED by default. Meaning PHP will emulate the prepare before execute sends it to the actual database. The time between emulated and non-emulated is normally negligible unless working with an external database (not localhost), such as on a cloud, that may have an abnormally high ping rate.
The caching depends on your MySQL settings in my.cnf as well, but MySQL optimization outside the scope of this post.
<?php
$pdo = new \PDO($connection_string);
$pdo->setAttribute( \PDO::ATTR_EMULATE_PREPARES, false );
?>
So keep this in mind since mysqli_ does not provide an API for client side emulation and is always going to use MySQL for preparing statements.
http://www.php.net/manual/en/mysqli.quickstart.prepared-statements.php
Despite having similar features there are differences and you may need features that one API provides while the other does not. See PHP's reference on choosing one API over the other: http://www.php.net/manual/en/mysqlinfo.api.choosing.php
So this pretty much goes along with what you asked with defining your statements application-wide, as cacheable queries would be cached on the MySQL server, and wouldn't need to be prepared application-wide.
The other benefit is that exceptions in your Query would be thrown at prepare() instead of execute() which aids in development to ensure your Queries are correct.
Regardless there is no real world performance benefits of using prepare or not.
Another benefit of prepared statements is working with Transactions if you use InnoDB for MySQL. You can start a transaction, insert a record, get the last insert id, update another table, delete from another, and if anything fails along the way you can rollBack() to before the transaction took place. Otherwise commit the changes if you choose to. For example working with a new order and setting the user's last order column to the new order id, and delete a pending order, but the supplied payment type did not meet the criteria for placing orders from the order_flags table, so you can rollBack() and show the user a friendly error message.
As for security, I am rather baffled no one touched on this. When sending any user supplied data to ANY system including PHP and MySQL, sanitize and standardize it.
Yes prepared statements do provide some security when it comes to escaping the data but it is NOT 100% bullet proof.
So always using prepared statements is far more beneficial than not with no real performance loss, and some benefits with caching, but you should still sanitize your user supplied data.
One step is to typecast the variables to the desired data type you are working with. Using objects would further ease this since you work within a single Model for the data types as opposed to having to remember it each time you work with the same data.
To add on to the above you should look into a database abstraction layer that uses PDO.
For example Doctrine DBAL: http://docs.doctrine-project.org/projects/doctrine-dbal/en/latest/reference/query-builder.html
The added benefits of working with a DBAL+PDO are that
You can standardize and shorten the amount of work you have to do.
Aid in sanitization of user supplied data
Easily manipulate complex queries
Use nested transactions
Easily switch between databases
Your code becomes more portable and usable in other projects
For example I extended PDO and overrode the query(), fetchAll(), and fetch() methods so that they would always use prepared statements and so that I could write SQL statements inside fetch() or fetchAll() instead of having to write everything out again.
EG:
<?php
$pdo = new PDOEnhanced( $connection );
$pdo->fetchAll( "SELECT * FROM foo WHERE bar = 'hi'", PDO::FETCH_OBJ );
//would automatically provide
$stmt = $pdo->prepare( "SELECT * FROM foo WHERE bar=?" );
$stmt->execute( array( 'hi' ) );
$resultSet = $stmt->fetchAll( PDO::FETCH_OBJ )
?>
As for people suggesting that mysql_* style, is much easier to just replace with mysqli_* API. It is not the case. A large portion of mysql_* functions were left out or had arguments changes with mysqli_*
See: http://php.net/manual/en/mysqli.summary.php
You can however get a converter released by Oracle to ease the process: https://wikis.oracle.com/display/mysql/Converting+to+MySQLi
Keep in mind that it is a file source text parser and is not 100% accurate so validate the changes before merging them. It will also add a significant amount of overhead for the globals it creates.
I wonder if those prepared statements of PDO really increase security, or if they are just a "cheap" text-replace in the query. The point of prepared statements actually is, that whatever gets inserted as parameter, will not be parsed by the DBMS as part of the instructions itself, so a parameter like
"'; DROP TABLE foobar;"
has no effect and does not break the query. Does anyone know this in detail? I thought to use PDO with prepared statements for preventing sql injection. It turns out that they are hard to use (and don't even work, at least on my local machine), so I want to find this out before wasting much more time with PDO ;-)
Creating a prepared statement sends the query-with-wildcards to the server for parsing, and returns a token to call that statement.
A call merely involves sending the data bound to every parameter. This means there will be no parsing of the data (because it's not part of a query string), and that the structure of the query is fixed when the prepared statement is parsed and cannot be altered by injection.
So, yes, a prepared statement definitely increases safety.
It also means you do not have to incur the parsing overhead if you reuse a prepared statement for several requests.
Yes, they increase security. PDO or MySQLi also increases speed versus the regular MYSQL methods in PHP because the data is passed in a more compact form.
I'm re-engineering a PHP-driven web site which uses a minimal database. The original version used "pseudo-prepared-statements" (PHP functions which did quoting and parameter replacement) to prevent injection attacks and to separate database logic from page logic.
It seemed natural to replace these ad-hoc functions with an object which uses PDO and real prepared statements, but after doing my reading on them, I'm not so sure. PDO still seems like a great idea, but one of the primary selling points of prepared statements is being able to reuse them… which I never will. Here's my setup:
The statements are all trivially simple. Most are in the form SELECT foo,bar FROM baz WHERE quux = ? ORDER BY bar LIMIT 1. The most complex statement in the lot is simply three such selects joined together with UNION ALLs.
Each page hit executes at most one statement and executes it only once.
I'm in a hosted environment and therefore leery of slamming their servers by doing any "stress tests" personally.
Given that using prepared statements will, at minimum, double the number of database round-trips I'm making, am I better off avoiding them? Can I use PDO::MYSQL_ATTR_DIRECT_QUERY to avoid the overhead of multiple database trips while retaining the benefit of parametrization and injection defense? Or do the binary calls used by the prepared statement API perform well enough compared to executing non-prepared queries that I shouldn't worry about it?
EDIT:
Thanks for all the good advice, folks. This is one where I wish I could mark more than one answer as "accepted" — lots of different perspectives. Ultimately, though, I have to give rick his due… without his answer I would have blissfully gone off and done the completely Wrong Thing even after following everyone's advice. :-)
Emulated prepared statements it is!
Today's rule of software engineering: if it isn't going to do anything for you, don't use it.
I think you want PDO::ATTR_EMULATE_PREPARES. That turns off native database prepared statements, but still allows query bindings to prevent sql injection and keep your sql tidy. From what I understand, PDO::MYSQL_ATTR_DIRECT_QUERY turns off query bindings completely.
When not to use prepared statements? When you're only going to be running the statement once before the db connection goes away.
When not to use bound query parameters (which is really what most people use prepared statements to get)? I'm inclined to say "never" and I'd really like to say "never", but the reality is that most databases and some db abstraction layers have certain circumstances under which they won't allow you to bind parameters, so you're forced to not use them in those cases. Any other time, though, it will make your life simpler and your code more secure to use them.
I'm not familiar with PDO, but I'd bet it provides a mechanism for running parametrized queries with the values given in the same function call if you don't want to prepare, then run as a separate step. (e.g., Something like run_query("SELECT * FROM users WHERE id = ?", 1) or similar.)
Also, if you look under the hood, most db abstraction layers will prepare the query, then run it, even if you just tell it to execute a static SQL statement. So you're probably not saving a trip to the db by avoiding explicit prepares anyhow.
Prepared statements are being used by thousands of people and are therefore well-tested (and thus one can infer they are reasonably secure). Your custom solution is only used by you.
The chance that your custom solution is insecure is pretty high. Use prepared statements. You have to maintain less code that way.
The benefits of prepared statements are as follows:
each query is only compiled once
mysql will use a more efficient transport format to send data to the server
However, prepared statements only persist per connection. Unless you're using connection pooling, there would be no benefit if you're only doing one statement per page. Trivially simple queries would not benefit from the more efficient transport format, either.
Personally I wouldn't bother. The pseudo-prepared statements are likely to be useful for the safe variable quoting they presumably provide.
Honestly, I don't think you should worry about it. However, I remember that a number of PHP data access frameworks supported prepare statement modes and non-prepare statement modes. If I remember correctly, PEAR:DB did back in the day.
I have ran into the same issue as you and I had my own reservations, so instead of using PDO I ended up writing my own light-weight database layer that supported prepares and standard statements and performed correct escaping (sql-injection prevention) in both cases. One of my other gripes with prepares is that sometimes it is more efficient to append some non-escapable input to a statement like ... WHERE id IN (1, 2, 3...).
I don't know enough about PDO to tell you what other options you have using it. However, I do know that PHP has escaping functions available for all database vendors it supports and you could roll your own little layer on top of any data access layer you are stuck with.