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Editorial Team
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Asked: 2026-05-30T19:59:45+00:00

I have seen in many articles on Sql Server which states that when we

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I have seen in many articles on Sql Server which states that when we are writing a query we should avoid using NOT and LIKE operator in our query because indexing is not applied on it.

eg.

  SELECT [CityId]
      ,[CityName]
      ,[StateId]
  FROM [LIMS].[dbo].[City]
  WHERE CityId NOT IN(1, 2)

I executed above query and found that indexing was getting used to filter the records.
Following is the execution plan, which clearly shows Clustured Index seek. This clearly violates what I used to think and read.

enter image description here

Was my previous understanding incorrect ?

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1 Answer

  1. Editorial Team

    That indexing does not work with LIKE and NOT operators is just a rule of thumb. SQL Server (or any competent RDBMS, for that matter) will use the best algorithm it can in most cases. So, if you could manually seek an index, so could SQL Server.

    In the particular example you provided, it is unclear whether a seek is any more efficient than a scan because most of the records are going to be returned anyhow. So, I wouldn’t read much into that particular execution plan.

    Bottom line: Learn and understand how your database system internally organizes data and indices so you won’t have to rely on rules of thumb.

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