Understanding Query Performance with the Query Plan
If you aren’t familiar with database indexes, Wikipedia has a pretty good definition,[35] but in essence, an index is a data structure created inside the database that speeds up query operations. Usually, databases use advanced data structures like B-trees to find the data you’re looking for without examining every single row in a table.
If you are familiar with indexes, you might only be familiar with the type of indexes that can be created by Active Record’s Migrations API. This API provides a “lowest common denominator” approach. The best we can do is create an index on last_name, first_name, and email. Doing so won’t actually help us because of the search we are doing. We need to match ...
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