Bucket aggregations (terms, histogram) in Elasticsearch - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a terms aggregation in Elasticsearch?

A terms aggregation groups documents by unique values in a field, like sorting items into buckets based on categories or tags.

beginner

How does a histogram aggregation work?

It groups numeric values into fixed-size intervals (buckets), like putting ages into ranges: 0-10, 11-20, etc.

intermediate

What is the purpose of the size parameter in a terms aggregation?

It limits how many top unique terms (buckets) to return, like showing only the top 5 most common categories.

intermediate

In a histogram aggregation, what does the interval parameter control?

It sets the width of each bucket, deciding how big each numeric range is, like grouping sales by every $100.

advanced

Can you combine bucket aggregations in Elasticsearch?

Yes, you can nest bucket aggregations to group data in multiple layers, like grouping by category then by price ranges.

What does a terms aggregation group documents by?

A Unique values in a field

B Fixed numeric ranges

C Document length

D Date ranges

Terms aggregation groups documents by unique values in a specified field.

Which parameter controls the number of buckets returned in a terms aggregation?

A size

B interval

C from

D order

The size parameter limits how many top buckets are returned.

What does the histogram aggregation's interval parameter define?

A Number of buckets

B Bucket size (range width)

C Sorting order

D Field name

Interval sets the width of each numeric bucket.

Which aggregation would you use to group documents by price ranges?

A terms aggregation

B filter aggregation

C histogram aggregation

D date histogram

Histogram aggregation groups numeric values into ranges, perfect for price ranges.

Can bucket aggregations be nested inside each other?

A No, only one level allowed

B Only for terms aggregation

C Only for histogram aggregation

D Yes, to create multi-level grouping

Bucket aggregations can be nested to group data in multiple layers.

Explain how terms and histogram bucket aggregations differ and give a real-life example for each.

Think about sorting items by category vs. grouping numbers into intervals.

Describe how you would use nested bucket aggregations to analyze sales data by region and price range.

Imagine sorting sales first by location, then by price groups.

Practice

1.

What does the terms aggregation do in Elasticsearch?

easy

A. Sorts documents by date in ascending order

B. Groups documents by unique values of a field and counts them

C. Filters documents based on a numeric range

D. Calculates the average value of a numeric field

Solution

1. Step 1: Understand the purpose of terms aggregation

   The terms aggregation groups documents by unique values of a specified field.

2. Step 2: Recognize the output of terms aggregation

   It counts how many documents fall into each unique value group.

3. Final Answer:

   Groups documents by unique values of a field and counts them -> Option B

4. Quick Check:

   terms aggregation = grouping by unique values [OK]

Hint: Remember: terms = group by unique values and count [OK]

Common Mistakes:

• Confusing terms with filtering
• Thinking terms sorts documents
• Mixing terms with metric aggregations

2.

Which of the following is the correct syntax for a histogram aggregation on a field named price with interval 50?

{
  "aggs": {
    "price_ranges": {
      "histogram": {
        "field": "price",
        "interval": 50
      }
    }
  }
}

easy

A. Correct as shown

B. Use "interval": "50" (string instead of number)

C. Use "terms" instead of "histogram"

D. Place "interval" outside "histogram" block

Solution

1. Step 1: Check the structure of histogram aggregation

   The histogram aggregation requires a field and a numeric interval inside its block.

2. Step 2: Verify the given JSON syntax

   The example correctly places field and interval inside the histogram object with interval as a number.

3. Final Answer:

   Correct as shown -> Option A

4. Quick Check:

   Histogram syntax with numeric interval = correct [OK]

Hint: Interval must be a number inside histogram block [OK]

Common Mistakes:

• Using string instead of number for interval
• Confusing terms and histogram aggregations
• Placing interval outside histogram object

3.

Given this aggregation query:

{
  "aggs": {
    "by_category": {
      "terms": { "field": "category.keyword" }
    }
  }
}

What will the aggregation return?

medium

A. The average value of the category field

B. A histogram of categories grouped by numeric ranges

C. A list of unique categories with document counts for each

D. A filtered list of documents matching category.keyword

Solution

1. Step 1: Identify the aggregation type and field

   The query uses a terms aggregation on the category.keyword field, which groups by unique values.

2. Step 2: Understand the output of terms aggregation

   It returns buckets for each unique category with counts of documents in each bucket.

3. Final Answer:

   A list of unique categories with document counts for each -> Option C

4. Quick Check:

   Terms aggregation output = unique value buckets with counts [OK]

Hint: Terms aggregation returns unique values with counts [OK]

Common Mistakes:

• Thinking histogram groups string fields
• Expecting average instead of counts
• Confusing filtering with aggregation

4.

Identify the error in this aggregation query:

{
  "aggs": {
    "price_buckets": {
      "histogram": {
        "field": "price",
        "interval": "100"
      }
    }
  }
}

medium

A. The field name "price" is invalid

B. Missing "size" parameter for histogram

C. Histogram aggregation cannot be nested inside aggs

D. The interval value should be a number, not a string

Solution

1. Step 1: Check the type of the interval parameter

   The interval must be a numeric value, but here it is given as a string "100".

2. Step 2: Understand impact of wrong interval type

   Using a string instead of a number causes a syntax error or unexpected behavior in Elasticsearch.

3. Final Answer:

   The interval value should be a number, not a string -> Option D

4. Quick Check:

   Interval must be numeric, not string [OK]

Hint: Interval must be numeric, not quoted string [OK]

Common Mistakes:

• Using string instead of number for interval
• Assuming field name is wrong without checking
• Thinking histogram can't be inside aggs

5.

You want to group sales data by price ranges of 100 units and then within each price range, group by product category. Which aggregation structure should you use?

hard

A. { "aggs": { "price_ranges": { "histogram": { "field": "price", "interval": 100 }, "aggs": { "by_category": { "terms": { "field": "category.keyword" } } } } } }

B. { "aggs": { "by_category": { "terms": { "field": "category.keyword" }, "aggs": { "price_ranges": { "histogram": { "field": "price", "interval": 100 } } } } } }

C. { "aggs": { "price_ranges": { "terms": { "field": "price" }, "aggs": { "by_category": { "histogram": { "field": "category.keyword", "interval": 100 } } } } } }

D. { "aggs": { "by_category": { "histogram": { "field": "category.keyword", "interval": 100 }, "aggs": { "price_ranges": { "terms": { "field": "price" } } } } } }

Solution

1. Step 1: Identify the primary grouping by price ranges

   The outer aggregation should be a histogram on the price field with interval 100 to group sales by price ranges.

2. Step 2: Nest the category grouping inside each price range bucket

   Inside each price range bucket, use a terms aggregation on category.keyword to group by product category.

3. Final Answer:

   Aggregation with histogram on price and nested terms on category -> Option A

4. Quick Check:

   Histogram outer, terms nested = correct structure [OK]

Hint: Nest terms inside histogram for grouped sub-buckets [OK]

Common Mistakes:

• Reversing the order of aggregations
• Using terms for numeric price instead of histogram
• Using histogram on keyword fields