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Showing posts from March, 2015

Temp Tables vs Table Varibles: The Great Debate

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) alwaysbe a nested loop join.

As long as the number of rows in the table variable are small…

Script Out SQL Row Constructors

A while back I got tired of having to type out the long strings to script out rows from a table, so I built a snippet which does it for you. It’s almost illegible to read, but it determines the columns of the table you choose and builds a string to output each row. I'll admit that this could be further refined to add in some more precise data type handling (perhaps casting date fields to a certain varchar format, or handling more obscure data types), but for most every day purposes, this does just fine. Also, when you copy/paste the results into a query window, you'll have to manually cut out the first "union all" to get it to run. These omissions are just me being lazy, but there's no reason they can't be done, and if you want to make them or wrap this in a procedure, I encourage you to do so. use go set nocount on go declare @string nvarchar(max) = ( --This creates a framework for each column in the chosen table, which then gets serialized and ap…