When a prefix query is executed in Elasticsearch, it searches for documents that contain a term starting with a specified prefix. The prefix query searches the inverted index for terms that match the specified prefix and returns any documents that contain a term with a matching prefix.
The matching process involves several steps:
1. Analysis: The search term is not analyzed and is treated as an exact prefix.
2. Term matching: The prefix query searches the inverted index for terms that start with the specified prefix. The query returns any documents that contain a term with a matching prefix in the specified field.
3. Scoring: Each document that matches the query is assigned a relevance score of 1.0, since the query matches the prefix exactly.
4. Sorting: The search results are sorted based on their relevance score, with the most relevant results appearing at the top of the list.
By default, the prefix query is case-sensitive, meaning that it will only match documents that contain a term with a matching prefix, including its case. If you need to perform a case-insensitive search, you can use a combination of the prefix query and the lowercase filter to convert the search term to lowercase before searching.
Overall, the prefix query provides a simple and efficient way to search for terms that start with a specified prefix in Elasticsearch, making it well-suited for searching fields that contain hierarchical or categorial data.