What are client-side prepared statements?

Question

Trying to learn something new - specifically trying to choose wether to use MySQLi or PDO for future projects when working with MySQL - I stumbled upon this page which shows an overview of options available to me.

At the bottom of this page is a table comparing functionality of the three main methods of communicating with mysql. In the row "API supports client-side Prepared Statements", it says that PDO supports this and MySQLi doesn't.

I know what prepared statements are. The answer to this question is a simple example of what I believe is server-side prepared statements. And PHP is a server-side language, which in turn should mean that it doesn't matter if client-side prepared statements are available or not. But that makes me wonder why that is even listed in the PHP manual then.

So what are client-side prepared statements?

Answer 1

Obviously, client-side prepared statements are statements that are prepared by the client, rather than the server.

PDO is a data-access abstraction layer that supports multiple DBMS interfaces (drivers), some of which support server-side prepared statements (e.g.: MySQL 4.1+), some of which don't (e.g.: MySQL 3).

In the event where the PDO driver does not support server-side prepared statements, PDO will emulate them on the client-side and use the generic query interface to execute them.

The reason why MySQLi doesn't support them is simple: MySQLi is a MySQL-specific extension, a RDBMS that indeed supports server-side prepared statements, so there is no reason to emulate them.

Answer 2

Like was said in the comments, in this case "client" refers to PHP and "server" to MySQL. PDO supports databases other than MySQL. Not all these databases/db drivers support prepared statements natively, and in those cases PDO will emulate these statements itself. MySQLi will not (I don't know for sure when it would have to do so - maybe when it's dealing with an old MySQL driver?).

One more factor you might want to consider - certain PHP frameworks require PDO and don't support mysqli.