Query times out when executed from web, but super-fast when executed from SSMS

Question

I\'m trying to debug the source of a SQL timeout in a web application that I maintain. I have the source code of the C# code behind, so I know exactly what code is running.

Answer 1

If using Entity Framework you must be aware that query parameters for string values are sent to database as nvarchar by default, if database column to compare is typed varchar, depending on your collation, query execution plan may require an "IMPLICIT CONVERSION" step, that forces a full scan. I could confirm it by looking in database monitoring in expensive queries option, which displays the execution plan.

Finally, a explanation on this behavior in this article: https://www.sqlskills.com/blogs/jonathan/implicit-conversions-that-cause-index-scans/