Why SQL Server go slow when using variables?

Question

I have a sql query that runs super fast, around one second, when not using variables, like:

WHERE id BETWEEN 5461094 and 5461097

But when I

Answer 1

It's because when the values are hard coded, it can look up the statistics it has on the data in the table, and figure out the best query to run. Have a look at the execution plans of each of these queries. It must be scanning when your using variables.

if the range is always small you might be able to use an index hint to help this.