Now, let’s start writing the first CTE! Nothing unusual here – as with every CTE, you define it by WITH they aren’t called WITH queries for nothing! You’ll need two CTEs, with the code looking like this:ĭATEDIFF (minute, login_start, login_end) AS minutesįirst, I’ll just mention that you have to have distinct usernames for this to work. If your task is to calculate the average time (in minutes) every user has spent logged in, how would you do it using CTEs? If you look at the table, you’ll notice that every username shows up at least once. Let’s imagine there’s a table named logins that stores login data. To spice this article up, I’ll finish by showing you two queries featuring CTEs, one of which is recursive. Then I’ll teach you how to use CTEs where the second CTE refers to the first one. Is it time for the MySQL community to raise the priority of the CTE feature requests for MySQL? Visit the links I gave above at, and add your voice by clicking the Affects Me button.I’ll start by explaining how to use two CTEs in one query. But there are quite a few other useful applications of this form of query, all the way up to fancy stunts like a query that generates a fractal design like the Mandelbrot Set. The most common example of a query solved with a recursive CTE is to query a tree of unknown depth. The CTE-style queries would allow us to share more advanced SQL queries with those that are being used by other brands of database, and do it with standard SQL instead of proprietary functions or tricks. Bug #20712 Please implement “with” statement (recursive form), June 2006.Bug #16244 SQL-99 Derived table WITH clause (CTE) (non-recursive form), January 2006.MySQL has been requested to support common table expressions using the WITH syntax for a long time: Only Informix among common RDBMS brands lacks support for WITH RECURSIVE, though Informix still supports recursive queries with the non-standard CONNECT BY syntax. H2 (date and version of support unknown).Teradata (date and version of support unknown, at least 2009).Fifteen years after it was defined in the SQL standard, almost every other SQL database of note has supported this feature: Why is this significant? It means that MySQL is now the only widely-used SQL implementation that does not support recursive queries. SQLite, another popular open-source SQL database, just released version 3.8.3, including support for recursive SQL queries using the WITH RECURSIVE syntax, in compliance with SQL:1999. But by focusing on the internals of the storage engine for so long, MySQL has fallen behind regarding support for advanced SQL features. Over the past few years, we’ve seen MySQL technology advance in leaps and bounds, especially when it comes to scalability.
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