Ben Nadel takes a moment to reflect on his mental model prepared statements in MySQL. And how he might use the CFQueryParam tag to go about safely creating prepared statements for SQL queries that use the IN clause with a dynamic set of parameters.
I've been using ColdFusion's
CFQueryParam for longer than I can remember. It seems like it's just always been there, protecting us against SQL-Injection attacks and helping to speed up query parsing and performance. But, I have to admit that my mental model for
CFQueryParam has always been a little bit fuzzy, especially when it comes to the
[list](https://www.bennadel.com/blog/425-coldfusion-cfqueryparam-list-attribute-is-sweeet.htm) attribute. Over the weekend, however, I was doing a lot of thinking about a particularly SQL query that I wrote; and, about its sub-par performance. I wanted to take a moment to think more deeply about prepared statements and open-ended
IN clauses in MySQL and ColdFusion.
To set the stage for this post, consider that I have a SQL query that gathers records based on an open-ended list of ID values. Something like this:
SELECT u.id, u.name, u.email FROM user u WHERE u.id IN ( ?????? ) ;
The list of IDs using in the
IN () clause is generated based on the results of a previous SQL query. A such, the list of IDs may contain a handful of values; it may contain hundreds of values; it's completely open-ended. Currently, this list of IDs is passed-through as raw SQL. Meaning, the parent
CFQuery tag is not producing a prepared statement - it does not use
To quote Adobe's article on the Hidden Power of
[CFQueryParam](https://coldfusion.adobe.com/2018/12/the-hidden-power-of-cfqueryparam/), using dynamic queries without prepared statements is problematic:
When the variable in our query is rendered by ColdFusion and the query is processed, SQL Server sees each version of the query as a completely different query and therefore has to create a new Execution Plan for it. Having an Execution Plan generated for every version of this query is expensive, in both processing overhead and resource utilization. If you run that query 1,000 times per day with a different ID each time, you have 1,000 copies of that same execution plan sitting in RAM on your SQL Server. Plus, the processing overhead of actually generating an Execution Plan is expensive, that's why SQL Server wants to cache it so that it doesn't have to do it every time. Repeatedly generating an Execution Plan can lead to higher CPU usage, and slower queries.
As such, in order to speed this SQL query up, I was considering converting the list of IDs to a
CFQueryParam tag. But, I know that some databases have a limit to the number of parameters that can be used in a single prepared statement. As such, I wanted to double-check my understanding of these limitations.
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