Exists query in Elasticsearch - Step-by-Step Execution

Concept Flow - Exists query

Start

↓

Send Exists Query

↓

Check if field exists in documents

↓

Return matching documents

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Return no matches

↓

End

The Exists query checks if a specific field is present in documents and returns those documents that have the field.

Execution Sample

Elasticsearch

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

This query finds all documents where the 'user' field exists.

Execution Table

Step	Action	Field Checked	Document Field Present?	Result
1	Send query to Elasticsearch	user	N/A	Query received
2	Check document 1	user	Yes	Document 1 matches
3	Check document 2	user	No	Document 2 does not match
4	Check document 3	user	Yes	Document 3 matches
5	Return all matching documents	user	N/A	Documents 1 and 3 returned

💡 All documents checked; only those with 'user' field are returned

Variable Tracker

Variable	Start	After Doc 1	After Doc 2	After Doc 3	Final
matched_documents	[]	[Doc1]	[Doc1]	[Doc1, Doc3]	[Doc1, Doc3]

Key Moments - 2 Insights

Why does the query only return documents that have the 'user' field?

Because the Exists query specifically checks if the 'user' field is present in each document, as shown in execution_table rows 2-4. Documents without the field are excluded.

What happens if no documents have the 'user' field?

The query returns no matches, as the check in execution_table would always be 'No', resulting in an empty matched_documents list.

Visual Quiz - 3 Questions

Look at the execution_table, which documents matched the query?

A Documents 2 and 3

B Documents 1 and 3

C Only Document 2

D All documents

💡 Hint

Check the 'Result' column in rows 2-4 of the execution_table.

At which step does the query decide a document does not match?

A Step 1

B Step 2

C Step 3

D Step 5

💡 Hint

Look at the 'Result' column in execution_table row 3.

If the field checked was changed to 'email', how would the matched_documents variable change?

A It would include documents with the 'email' field instead

B It would remain the same

C It would include all documents

D It would be empty regardless

💡 Hint

Refer to variable_tracker and understand it tracks documents matching the field checked.

Concept Snapshot

Exists query syntax:
{
  "query": {
    "exists": { "field": "fieldname" }
  }
}

Returns documents where the specified field exists.
Useful to filter documents that have a particular field.
Does not match documents missing that field.

Full Transcript

The Exists query in Elasticsearch checks if a specific field is present in documents. When you send this query, Elasticsearch looks at each document to see if the field exists. If it does, that document is included in the results. If not, it is skipped. For example, checking for the 'user' field returns only documents that have 'user'. This is useful to find documents containing certain information. The execution table shows each step: sending the query, checking documents, and returning matches. The variable tracker shows how matched documents build up as documents are checked. Common confusions include why only some documents return and what happens if no documents have the field. The quiz tests understanding of which documents match and how changing the field affects results.