Compound Queries in Elasticsearch
Introduction
Elasticsearch's Query DSL (Domain Specific Language) provides a rich and flexible mechanism to query data. Compound queries allow you to combine multiple queries in a single request, offering powerful ways to filter, score, and combine results based on various conditions.
Bool Query
The bool query is one of the most commonly used compound queries. It allows you to combine multiple queries using boolean logic.
The bool query supports four types of clauses:
must: All queries must match.filter: All queries must match, but these clauses do not contribute to scoring.should: At least one of these queries must match.must_not: None of these queries must match.
Example
{
"query": {
"bool": {
"must": [
{ "match": { "title": "Elasticsearch" } }
],
"filter": [
{ "term": { "status": "published" } }
],
"must_not": [
{ "range": { "publish_date": { "lte": "2020-01-01" } } }
],
"should": [
{ "match": { "tags": "search" } },
{ "match": { "tags": "analytics" } }
]
}
}
}
Constant Score Query
The constant_score query wraps another query and assigns a constant score to all documents matching the query, ignoring the relevance scores.
Example
{
"query": {
"constant_score": {
"filter": {
"term": { "status": "published" }
},
"boost": 1.5
}
}
}
Dis Max Query
The dis_max query is used to combine multiple queries and return the document score from the query with the highest score.
Example
{
"query": {
"dis_max": {
"queries": [
{ "match": { "title": "Elasticsearch" } },
{ "match": { "content": "Elasticsearch" } }
],
"tie_breaker": 0.7
}
}
}
Function Score Query
The function_score query allows you to modify the score of documents that are retrieved by a query. This is useful for customizing relevance scoring.
Example
{
"query": {
"function_score": {
"query": { "match": { "title": "Elasticsearch" } },
"boost": "5",
"functions": [
{
"filter": { "match": { "tags": "important" } },
"weight": 2
},
{
"filter": { "range": { "publish_date": { "gte": "2021-01-01" } } },
"weight": 3
}
],
"score_mode": "sum",
"boost_mode": "multiply"
}
}
}
Wrapping Up
Compound queries in Elasticsearch provide a powerful way to create complex search queries by combining multiple queries and controlling how they interact. Understanding and utilizing these queries allows for more precise and effective search solutions.