Is there any way to tell how long a MySQL query will take to run?

Other than running it to completion...

Is there some sort of progress you can monitor to see what operations are happening as your query is being processed that would give you a sense of how long it开发者_C百科's going to take, or at least what step it is on, what steps have happened, and which remain?

If yes, would this same tool help you identify the part of your query that is taking the longest?

I'm trying to get a better sense for what makes some queries take longer than others.

It's called profiling : http://dev.mysql.com/tech-resources/articles/using-new-query-profiler.html

MySQL has one built-in for you. : )

You can use explain to ask MySQL to show you why a function takes as longs as it does.

http://dev.mysql.com/doc/refman/5.0/en/explain.html

The idea is that it'll show you things like which indexes it uses, etc, which will help you to then optimise either the query or the table to make it quicker.

That's not a direct answer to your question, because it won't tell you real-time progress of the query, which is what you're asking for, but it does directly answer the last sentence of your question, and so it may actually be more useful to you for what you really want to know than any real-time progress report would be.