Bool query (must, should, must_not, filter) in Elasticsearch - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the must clause do in a Bool query?

The must clause requires that the query conditions inside it must be true for a document to match. Think of it as a strict rule that must be followed.

beginner

Explain the role of the should clause in a Bool query.

The should clause means that if the conditions inside it are true, the document scores higher, but it is not mandatory unless specified. It works like a nice-to-have feature.

beginner

What is the purpose of the must_not clause in a Bool query?

The must_not clause excludes documents that match the conditions inside it. It acts like a filter to remove unwanted results.

intermediate

How does the filter clause differ from must in a Bool query?

The filter clause also requires conditions to be true, but it does not affect the score of documents. It is used for fast filtering without scoring.

intermediate

Give a simple example of a Bool query using must, should, and must_not.

Example: Find documents where field1 must be 'apple', field2 should be 'red' (optional), and field3 must not be 'rotten'. This means documents must have 'apple', prefer 'red', and exclude 'rotten'.

In a Bool query, which clause excludes documents that match its conditions?

A filter

B must_not

C should

D must

The must_not clause excludes documents matching its conditions.

Which Bool query clause affects scoring of documents?

A filter

B must_not

C must

D none

The must clause affects scoring because it requires matching conditions.

What happens if a document matches a should clause but not a must clause?

A It is excluded

B It always matches

C It never matches

D It matches only if must is empty

Documents must match must clauses; should clauses boost score if must exists.

Which clause is best for fast filtering without scoring?

A filter

B should

C must

D must_not

Filter clause filters documents without affecting score.

If you want to exclude documents with field 'status' equal to 'inactive', which clause do you use?

A must_not

B should

C must

D filter

must_not excludes documents matching the condition.

Describe the four main clauses of a Bool query and their roles.

Think about which clauses require, prefer, exclude, or filter documents.

Explain how you would use a Bool query to find documents that must have a value, optionally have another, and exclude a third.

Use must for must-have, should for nice-to-have, must_not for no-go.

Practice

1. Which clause in an Elasticsearch bool query is used to exclude documents that match a condition?

easy

A. must

B. must_not

C. should

D. filter

Solution

1. Step 1: Understand bool query clauses

   The bool query has four main clauses: must (required), should (optional), must_not (exclude), and filter (limit without scoring).

2. Step 2: Identify exclusion clause

   The must_not clause excludes documents that match its conditions from the results.

3. Final Answer:

   must_not -> Option B

4. Quick Check:

   Exclude = must_not [OK]

Hint: Exclude with must_not clause in bool query [OK]

Common Mistakes:

• Confusing must_not with must
• Using should to exclude documents
• Thinking filter excludes documents

2. Which of the following is the correct syntax to add a must clause inside a bool query in Elasticsearch?

easy

A. "bool": { "must": [ { "match": { "field": "value" } } ] }

B. "bool": { "must": ( { "match": { "field": "value" } } ) }

C. "bool": { "must": "match": { "field": "value" } }

D. "bool": { "must": { "match": { "field": "value" } } }

Solution

1. Step 1: Recall bool must clause syntax

   The must clause expects an array of query objects inside the bool query.

2. Step 2: Check each option's syntax

   "bool": { "must": [ { "match": { "field": "value" } } ] } correctly uses an array with one match query object. The other options use incorrect types or missing brackets.

3. Final Answer:

   "bool": { "must": [ { "match": { "field": "value" } } ] } -> Option A

4. Quick Check:

   Must clause = array of queries [OK]

Hint: Must clause requires an array of query objects [OK]

Common Mistakes:

• Using object instead of array for must
• Missing brackets around match query
• Using parentheses instead of brackets

3. Given this bool query snippet, which documents will be matched?

{
  "bool": {
    "must": [{ "term": { "status": "active" }}],
    "should": [{ "term": { "role": "admin" }}],
    "must_not": [{ "term": { "banned": true }}]
  }
}

medium

A. Documents with status 'active' and role 'admin', excluding banned ones

B. Documents with status 'active' or role 'admin', including banned ones

C. Documents with role 'admin' only, excluding banned ones

D. Documents with status 'active', optionally role 'admin', excluding banned ones

Solution

1. Step 1: Analyze must clause effect

   The must clause requires documents to have status: active.

2. Step 2: Analyze should and must_not clauses

   The should clause means documents with role: admin are preferred but not required. The must_not clause excludes documents where banned is true.

3. Final Answer:

   Documents with status 'active', optionally role 'admin', excluding banned ones -> Option D

4. Quick Check:

   Must + optional should + exclude must_not = Documents with status 'active', optionally role 'admin', excluding banned ones [OK]

Hint: Must is required, should is optional, must_not excludes [OK]

Common Mistakes:

• Thinking should is required
• Ignoring must_not exclusion
• Confusing must and should roles

4. Identify the error in this bool query:

{
  "bool": {
    "must": { "match": { "title": "Elasticsearch" } },
    "filter": { "term": { "status": "published" } },
    "must_not": [ { "term": { "archived": true } } ]
  }
}

medium

A. "must" should be an array, not an object

B. "filter" cannot be used with "must_not"

C. "must_not" should be an object, not an array

D. The query is correct as is

Solution

1. Step 1: Check must clause format

   The must clause expects an array of query objects, but here it is given as a single object.

2. Step 2: Validate other clauses

   The filter and must_not clauses are correctly formatted as an object and an array respectively.

3. Final Answer:

   "must" should be an array, not an object -> Option A

4. Quick Check:

   Must clause = array required [OK]

Hint: Must clause must always be an array [OK]

Common Mistakes:

• Using object instead of array for must
• Thinking filter and must_not conflict
• Using array for must_not incorrectly

5. You want to find documents where the category is 'books' and the price is less than 20, but exclude those that are out of stock. Which bool query correctly implements this?

hard

A. { "bool": { "should": [ { "term": { "category": "books" } }, { "range": { "price": { "lt": 20 } } } ], "must_not": [ { "term": { "stock": "out" } } ] } }

B. { "bool": { "filter": [ { "term": { "category": "books" } }, { "range": { "price": { "lt": 20 } } } ], "must_not": { "term": { "stock": "out" } } } }

C. { "bool": { "must": [ { "term": { "category": "books" } }, { "range": { "price": { "lt": 20 } } } ], "must_not": [ { "term": { "stock": "out" } } ] } }

D. { "bool": { "must": { "term": { "category": "books" } }, "filter": { "range": { "price": { "lt": 20 } } }, "must_not": [ { "term": { "stock": "out" } } ] } }

Solution

1. Step 1: Identify required conditions

   Documents must have category: books and price < 20. Both are required, so they go in must as an array.

2. Step 2: Exclude out of stock documents

   Documents with stock: out must be excluded, so use must_not with an array of term queries.

3. Step 3: Check each option

   { "bool": { "must": [ { "term": { "category": "books" } }, { "range": { "price": { "lt": 20 } } } ], "must_not": [ { "term": { "stock": "out" } } ] } } correctly uses must array for required conditions and must_not array for exclusion. { "bool": { "filter": [ { "term": { "category": "books" } }, { "range": { "price": { "lt": 20 } } } ], "must_not": { "term": { "stock": "out" } } } } uses filter which is okay but must_not is an object, not array. { "bool": { "should": [ { "term": { "category": "books" } }, { "range": { "price": { "lt": 20 } } } ], "must_not": [ { "term": { "stock": "out" } } ] } } uses should which makes conditions optional, wrong here. { "bool": { "must": { "term": { "category": "books" } }, "filter": { "range": { "price": { "lt": 20 } } }, "must_not": [ { "term": { "stock": "out" } } ] } } uses must as object and filter as object, mixing styles incorrectly.

4. Final Answer:

   { "bool": { "must": [ { "term": { "category": "books" } }, { "range": { "price": { "lt": 20 } } } ], "must_not": [ { "term": { "stock": "out" } } ] } } -> Option C

5. Quick Check:

   Must array + must_not array for exclusion [OK]

Hint: Use must array for required, must_not array to exclude [OK]

Common Mistakes:

• Using should instead of must for required filters
• Using object instead of array for must or must_not
• Mixing filter and must incorrectly