01Aug 2016 by Grant Fritchey 1 Comment

There Is No Difference Between Table Variables, Temporary Tables and Common Table Expressions

SQL Server, SQL Server 2016, SQL Server 2017, T-SQL
I actually saw the above statement posted online. The person making the claim further stated that choosing between these three constructs was "personal preference" and didn't change at all the way SQL Server would choose to deal with them in a query. Let's immediately say, right up front, the title is wrong. Yes, there are very distinct differences between these three constructs. Yes, SQL Server will absolutely deal with these three constructs in different ways. No, picking which one is correct in a given situation is not about personal preference, but rather about the differences in behavior between the three. To illustrate just a few of the differences between these three constructs, I'll use variations of this query: SELECT * FROM Sales.Orders AS o JOIN Sales.OrderLines AS ol ON ol.OrderID = o.OrderID WHERE ol.StockItemID = 227; The…
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07Sep 2012 by Grant Fritchey 12 Comments

SQL Server vs. Oracle

PASS, Redgate Software, SQL Server, T-SQL
Just so we're clear, I use SQL Server. I like SQL Server. But, this doesn't mean I have anything against Oracle. It's fine. It's good. But, I know very little about it. However, throughout my career I've found myself needing to understand it better. Either because I'm trying to train Oracle people to better use SQL Server and I need to be able to speak a little of their language to facilitate translation. Or, because I'm defending SQL Server on some technical point that the Oracle people don't completely understand. Or, because I've said something stupid about Oracle in my ignorance. Now, you know how busy you are, and I know how busy I am, so I doubt either of us has the time we really need to learn Oracle…
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13Oct 2009 by Grant Fritchey 5 Comments

Table Variables Are Only in Memory: Fact or Myth

SQL Server, T-SQL
I keep seeing these concepts that have long been disproven, posted again and again on newsgroups as if they were valid information. The latest? Table variables are better because they're only in memory where as temporary tables write to the disk through tempdb. This one is abjectly wrong. I'm not even going to hedge with "it depends." From a macro point of view, there are only a few differences between temporary tables and table variables, statistics being the biggest. Temporary tables have 'em and table variables don't. Other than that, both will reside completely in memory or will swap out to the disk through tempdb, depending on their size. Some of the minor differences, and why you might want to use table variables over temporary tables, table variables won't cause a statement recompile while temporary tables will, table…
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