The ESR guideline is a practical way to reason about compound-index field order:

• Equality: fields matched with equality predicates often belong first.
• Sort: fields used to order results may follow.
• Range: range predicates often come after equality and sort fields when preserving index-supported sorting is important.

For example, a query that filters on exact status, sorts by creation time, and applies a date range may need careful index design. The best order depends on the exact query, selectivity, and whether avoiding an in-memory sort or narrowing the range is more important.

ESR is a guideline, not a mechanical rule. A highly selective range can sometimes justify a different order. Test realistic data and examine execution plans before settling on an index.

db.orders.createIndex({ status: 1, createdAt: -1 });

db.orders.find({ status: "delivered" })
  .sort({ createdAt: -1 })
  .limit(50)
  .explain("executionStats");