Why is SQL Server using index scan instead of index seek when WHERE clause contains parameterized values

Question

We have found that SQL Server is using an index scan instead of an index seek if the where clause contains parametrized values instead of string literal.

<

Answer 1

I guess first query is using predicate and second query is using seek predicate.

Seek Predicate is the operation that describes the b-tree portion of the Seek. Predicate is the operation that describes the additional filter using non-key columns. Based on the description, it is very clear that Seek Predicate is better than Predicate as it searches indexes whereas in Predicate, the search is on non-key columns – which implies that the search is on the data in page files itself.

For more details please visit:- https://social.msdn.microsoft.com/Forums/sqlserver/en-US/36a176c8-005e-4a7d-afc2-68071f33987a/predicate-and-seek-predicate