Exists query in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of an Exists Query

What will be the output count of documents matched by this Elasticsearch query if the index contains documents with and without the field user?

Elasticsearch

{
  "query": {
    "exists": {
      "field": "user"
    }
  }
}

A The count of documents that have the field 'user' present

B The count of documents that do NOT have the field 'user'

C All documents in the index regardless of the 'user' field

D An error because 'exists' query requires a 'value' parameter

💡 Hint

The 'exists' query matches documents where the specified field is present.

The 'exists' query in Elasticsearch returns documents that contain the specified field. It does not match documents missing that field or all documents.

🧠 Conceptual

intermediate

Purpose of Exists Query

What is the main purpose of the Elasticsearch 'exists' query?

A To find documents where a specific field exists and is not null

B To find documents where a field equals a specific value

C To find documents where a field is missing

D To update documents that have a specific field

💡 Hint

Think about what 'exists' means in the context of fields in documents.

The 'exists' query is used to find documents that contain a particular field with any value, meaning the field is present and not null.

🔧 Debug

advanced

Why does this Exists Query fail?

Given this query, why does Elasticsearch return a syntax error?

Elasticsearch

{
  "query": {
    "exists": {
      "field" "user"
    }
  }
}

A The 'exists' query requires a 'value' parameter, which is missing

B Missing colon between 'field' and 'user' causes a JSON syntax error

C The field name 'user' must be in an array

D The 'exists' query cannot be used inside 'query' object

💡 Hint

Check the JSON syntax carefully around the 'field' key.

The JSON syntax requires a colon between keys and values. Missing the colon causes a syntax error.

❓ Predict Output

advanced

Output of Exists Query with Nested Fields

What documents will this query match if the index contains nested objects under 'comments' and some have 'author' fields?

Elasticsearch

{
  "query": {
    "nested": {
      "path": "comments",
      "query": {
        "exists": {
          "field": "comments.author"
        }
      }
    }
  }
}

A Documents that have the 'comments' field but no 'author' inside it

B Documents that have the 'author' field anywhere in the document

C Documents that have at least one 'comments' nested object with an 'author' field

D All documents regardless of 'comments' or 'author' fields

💡 Hint

The 'nested' query targets nested objects and the 'exists' query checks for field presence inside those objects.

The query matches documents where at least one nested 'comments' object contains the 'author' field.

🧠 Conceptual

expert

Behavior of Exists Query on Null and Empty Fields

Which statement correctly describes how the Elasticsearch 'exists' query treats fields with null or empty string values?

A Empty string values cause the 'exists' query to fail with an error

B Fields with null values match the 'exists' query because the field is present

C The 'exists' query matches only fields with non-empty string values

D Fields with null values are considered missing and will NOT match the 'exists' query

💡 Hint

Think about how Elasticsearch indexes null values and what 'exists' means.

Elasticsearch does not index fields with null values, so they are treated as missing and do not match the 'exists' query. Empty strings are indexed and do match.