What are parameterized queries explained in plain English?

Question

Can anybody explain me in plain English what parametrized queries are and how to implement it in PHP for a MySQL database to avoid SQL injection?

Answer 1

The prepared statements and stored procedures section of the PHP manual, whilst it relates specifically to PDO, covers this well when it says:

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 it's 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).

If you're after specific example of how to use them, the above linked page also includes code samples.