Towering Queries

There seems to be a lot of confusion around the differences between  temp tables and table variables (in the classic sense; I'm not talking about in memory table types or anything here). Some people say you should only use table variables. Some people say you should only use temp tables. Most people caution a more nuanced approach. Here I want to cover what I think are the biggest issues in an attempt to shed some light on this surprisingly tricky topic. Statistics This is usually the most important factor when considering which one to use. It boils down to two facts, and everything else flows from these: Temp Tables maintain statistics, Table Variables do not. Table Variables Because table variables maintain no statistics, the Query Optimizer always assumes the contain exactly one row. As a result, any joins against a table variable, unless explicitly told to behave otherwise will (probably) always be a nested loop join. As long as the number of rows in the table varia

I just spent several hours trying to figure this out, so I felt it was worth posting here too. If you are installing Master Data Services on Windows 10, there are a bunch of  IIS Web Application Requirements  you have to satisfy in IIS, or the Master Data Services Configuration Manager will say you're missing all kinds of services and roles. Most of the documentation relates to using Windows Server, since that's usually where SQL is running. But for a localhost instance you might have for testing, it's probably not. And in my case, it's on Windows 10 home   edition . That last fact is what threw me most because even after enabling all the features I could find on the list in the link above, it still didn't work. That's because by default, you need Windows 10 professional edition  to use Windows Authentication, and MDS requires Windows Authentication enabled for IIS to work. So you can either upgrade to Pro or manually enable that feature through the command

A few co-workers asked me to explain some of the nuances of different join types (outer joins in particular). I've always reached for Venn diagrams in the past, but I was trying to think of a better way to get the information across. Whether or not I succeeded, I'll let you be the judge. I'm not going to do much in the way of explaining each of the diagrams, but I will label each diagram. I also included a diagram at the end of a common trick for inserting only rows which don't already exist in the target table (using a left outer join, and checking where the right values are null). Please feel free to use this code and the diagrams if you think they're useful. If you do, it would be nice to credit me with them, but I'm hardly going to get mad if you don't. I'd much rather there just be good training materials out there. The Code if object_id('tempdb.dbo.#Cards') is not null drop table #Cards create table #Cards ( NumericValue tinyint n