$bucket groups documents into explicitly defined ranges. $bucketAuto attempts to create a requested number of buckets with approximately balanced document counts and data-dependent boundaries.

Use $bucket when boundaries have business meaning, such as fixed price bands. Use $bucketAuto for exploratory distributions. Consider how missing, null, and nonnumeric values are handled, and use a default bucket when appropriate for values outside configured boundaries.

db.products.aggregate([
  {
    $bucket: {
      groupBy: "$currentPrice",
      boundaries: [0, 1000, 5000, 10000, 20000],
      default: "outside-defined-ranges",
      output: { productCount: { $sum: 1 }, averagePrice: { $avg: "$currentPrice" } }
    }
  },
  { $sort: { _id: 1 } }
]);