Partial Matchingedit

A keen observer will notice that all the queries so far in this book have operated on whole terms. To match something, the smallest unit had to be a single term. You can find only terms that exist in the inverted index.

But what happens if you want to match parts of a term but not the whole thing? Partial matching allows users to specify a portion of the term they are looking for and find any words that contain that fragment.

The requirement to match on part of a term is less common in the full-text search-engine world than you might think. If you have come from an SQL background, you likely have, at some stage of your career, implemented a poor man’s full-text search using SQL constructs like this:

    WHERE text LIKE "%quick%"
      AND text LIKE "%brown%"
      AND text LIKE "%fox%" 

*fox* would match “fox” and “foxes.”

Of course, with Elasticsearch, we have the analysis process and the inverted index that remove the need for such brute-force techniques. To handle the case of matching both “fox” and “foxes,” we could simply use a stemmer to index words in their root form. There is no need to match partial terms.

That said, on some occasions partial matching can be useful. Common use cases include the following:

  • Matching postal codes, product serial numbers, or other not_analyzed values that start with a particular prefix or match a wildcard pattern or even a regular expression
  • search-as-you-type—displaying the most likely results before the user has finished typing the search terms
  • Matching in languages like German or Dutch, which contain long compound words, like Weltgesundheitsorganisation (World Health Organization)

We will start by examining prefix matching on exact-value not_analyzed fields.