til/rails/query-a-single-value-from-the-database.md

Query A Single Value From The Database

In a Rails context, most database interactions tend to happen through the ORM (e.g. Book.find("123")). There is a general purpose escape hatch that lets you execute a SQL statement directly against the DB -- execute. The resulting value of execute, however, tends to be a little clunky to work with.

If you just need a single value from the DB, use the select_value method.

> statement = "select gen_random_uuid()"
> ActiveRecord::Base.connection.select_value(statement)
   (5.0ms)  select gen_random_uuid()
 => "abc2e780-f442-418b-afa3-56f0ccd0a903"

This is the cleanest way to get the result of a "single value" query.

If you happen to pass in a query that results in more than one row or column, it will return the value of the first column from the first row.