Select * Syndrome

NoSomething that I have seen lately over and over again and even ran into this morning is a practice that I would say is a pretty bad habit in SQL….the dreaded Select * syndrome

This method is heavily used for adhoc querying and I’ve seen it used in some troubleshooting scenarios but in my case I don’t have room for it in a production environment embedded in functions, procedures, or views.

To me it is a wasteful tactic in bringing back what is needed; it can produce unwanted scans or look-ups when in some cases all that is needed is index tuning. I’m a big fan of bringing back what you need instead of bringing back a tremendous amount of data. One can also make an argument for all the unused overhead it can produce.

I cannot begin to tell you the many times of deploying something out and then to find out the schema has changed and the select * in a view that was left in place years ago is my culprit from years of past coding that has been done.

For example; one that I have seen within the past couple of months is a view:

Select *

From table 1

Union All

Select *

From table2

This was being used quite frequently and is just asking for trouble and poor performance. There will always be excuses as to why it wasn’t done differently but in the end you will go back in and clean it up so it is best to think the process you are working on through in the beginning instead of the end.

Can I ever use it?

Sure….I’ve seen it used in If Exists clauses many times over and from my research and what I know SQL does not count this in the execution plans; if you leverage SQL the correct way it is more than powerful to handle what you need.

Tools to fight the good fight………

My source control is TFS and I like the newest version as you can set up controls that if a Select * is found it will break the build in dev forcing it to be resolved

If you haven’t already downloaded the free version check out the SQL Plan Explorer provided by SQL Sentry. Execute the tasks different ways with the select * and with pulling back designated columns and review the execution plan; you will be surprised at the outcome, and if you are old school that is fine too – analyze it in SSMS and see what you find.

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