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…

Square marquee

For those of you who may not have known, there’s a cool trick you can do in Visual Studio or SSMS; the alt-drag marquee. Many of these functions can be handled with fine and replace with or without regular expressions, but sometimes those are more trouble than it’s worth.

The basics of alt-drag are this. Say I have a block of text, such as a comment block of a procedure which I want to replace all at once. Hold alt and drag to the bottom right, and you get a marquee area which respects x/y coordinates rather than just lines and indentation.


Now the cool part. If you’ve ever used copy-paste with these marquees, you’ll find they work… oddly. However like any good Jedi, you can turn your enemies weakness into your strength.

Say for example, I forgot to type select statements for a derived table like this:


You could use find replace to replace “all” with “all select’, you could use a series of copy/paste commands and down arrow keys, or this:

Create a zero-width vertical marquee and start typing. Every text line which is crossed by the marquee will begin typing there (it works with ctrl-v_ as well.

Note, you can also hold alt+shift and use the arrow keys to make a square marquee as well.

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