Consider the queries in the options below and the following information:For these queries, assume that...

When querying Large Data Volumes (LDV), Salesforce relies on the Query Optimizer to decide if an index can be used. A query is considered "optimized" or "selective" if it uses an indexed field in the WHERE clause and filters the result set below a specific threshold (typically 10% of the first million records).

Option A is optimized because it filters on Customer_Number__c, which is marked as an External ID. Salesforce automatically creates a custom index for any field marked as an External ID or Unique. Even though the query also includes a non-selective filter (Name != ''), the presence of the indexed External ID field allows the optimizer to perform an index scan rather than a full table scan.

Option D is optimized because it filters by the Id field using the IN operator. The Id field is the primary key and is always indexed. Filtering by a collection of IDs is one of the most efficient ways to retrieve records in a large environment.

Options B and C are not optimized. IsDeleted is not an indexed field, and the Query Optimizer generally ignores IsDeleted = false filters when calculating selectivity. Filtering for Name != NULL or Name != '' (Option C) is considered a "negative" filter and typically results in a full table scan because it does not narrow the search results enough to utilize an index efficiently.