A wildcard query is a query type in Elasticsearch that is used to search for documents that contain terms that match a specified pattern using wildcards. The wildcard query is often used for searching fields that contain text that may vary in spelling or contain variations that cannot be captured by a fuzzy query.
When a wildcard query is executed, Elasticsearch searches the inverted index for terms that match the specified pattern using wildcards. The wildcard character `*` matches zero or more characters, while the wildcard character `?` matches exactly one character. The wildcard query returns any documents that contain a term that matches the specified pattern.
Here’s an example of a wildcard query in Elasticsearch:
GET /my_index/_search
{
"query": {
"wildcard": {
"title": {
"value": "elasticsearch*"
}
}
}
}
In this example, we are searching the `title` field in the `my_index` index for terms that match the pattern “elasticsearch*”, using the wildcard character `*`. The wildcard query will return any documents that contain a term in the `title` field that matches the specified pattern.
The wildcard query can also be used in combination with other query types, such as the bool query, to construct more complex search queries. By allowing for searching for terms that match a specified pattern using wildcards, the wildcard query provides a powerful and flexible way to search for text in Elasticsearch.
It’s important to note that wildcard queries can be computationally expensive and may not be suitable for large datasets or high-traffic applications. Additionally, wildcard queries can be less precise than other query types, such as the term or match query, because they match a broader range of terms.