C100DEV Aggregation Framework Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  $mean

  Why it's wrong here

  The $mean operator does not exist in the MongoDB aggregation framework. Users often confuse it with standard statistical terminology, but $avg is the correct operator provided by the engine. Using an invalid operator will result in a syntax error when the pipeline is executed.

• ✗

  $sum

  Why it's wrong here

  The $sum operator is used to add up numerical values, not to calculate the mean. While finding the average involves sum and count, $avg is the shorthand operator provided for this purpose. Using $sum alone would produce the total, which is functionally different from the average.

• ✓

  $avg

  Why this is correct

  $avg is the standard accumulator used to calculate the arithmetic mean. It automatically handles the summation and division by the count of documents, providing a clean and efficient way to summarize numeric trends within the aggregation pipeline's grouping phase.

• ✗

  $median

  Why it's wrong here

  The $median operator is not a standard accumulator in the aggregation framework for general use. MongoDB provides other mechanisms for finding percentiles, but $median is not the correct choice for calculating a simple average. This would lead to incorrect results or syntax errors.