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Asked: 2026-05-11T06:24:29+00:00

Given this linq query against an EF data context: var customers = data.Customers.Where(c =>

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Given this linq query against an EF data context:

var customers = data.Customers.Where(c => c.EmailDomain.StartsWith(term))

You’d expect it to produce SQL like this, right?

SELECT {cols} FROM Customers WHERE EmailDomain LIKE @term+’%’

Well, actually, it does something like this:

SELECT {cols} FROM Customer WHERE ((CAST(CHARINDEX(@term, EmailDomain) AS int)) = 1)

Do you know why?

Also, replacing the Where selector to:

c => c.EmailDomain.Substring(0, term.Length) == term

it runs 10 times faster but still produces some pretty yucky SQL.

NOTE: Linq to SQL correctly translates StartsWith into Like {term}%, and nHibernate has a dedicated LikeExpression.

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1 Answer

  1. The reason is that CharIndex is a lot faster and cleaner for SQL to perform than LIKE. The reason is, that you can have some crazy ‘LIKE’ clauses. Example:

    SELECT * FROM Customer WHERE EmailDomain LIKE 'abc%de%sss%'

    But, the ‘CHARINDEX’ function (which is basically ‘IndexOf’) ONLY handles finding the first instance of a set of characters… no wildcards are allowed.

    So, there’s your answer 🙂

    EDIT: I just wanted to add that I encourage people to use CHARINDEX in their SQL queries for things that they didn’t need ‘LIKE’ for. It is important to note though that in SQL Server 2000… a ‘Text’ field can use the LIKE method, but not CHARINDEX.

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