How to use select....as and concat in rails 5 - ruby-on-rails

Question

I have a table called Student, the student table contains the id, first_name and last_name. I am trying to select and concatenate first_name and last_name and display the column as "Name". This is my query:
Student.select("concat(first_name, ' ', last_name) as 'Name'").find(201410204)
but it returns
SELECT concat(first_name, ' ', last_name) as 'Name' FROM `students` WHERE `students`.`id` = 201410204 LIMIT 1
#<Student id: nil>
but when i try to paste the query inside mysql workbench it return the student name that has the id 201410204 and the column name is "Name".
Click to see the result of the query
What's the problem about my code? Thanks

Answer 1

You need to select the id as well:
Student.select(:id, "CONCAT(first_name,' ',last_name) as name").find(201410204)
2.4.1 :073 > Student.select(:id, "CONCAT(first_name,' ',last_name) as name").find(23000)
Student Load (0.9ms) SELECT "students"."id", CONCAT(first_name,' ',last_name) as name FROM "students" WHERE "students"."id" = $1 LIMIT $2 [["id", 23000], ["LIMIT", 1]]
=> #<Student id: 23000, name: "Joe Blow">

Answer 2

Let me give you two solutions, one by using the power of rails and other using the scalability of rails.
1) (Using power of rails)
In the Student model create a method named full_name and concatenate first_name and last_name.
class Student < ActiveRecord::Base
.....
def full_name
"#{try(:first_name)} #{try(:last_name)}".to_s
end
.....
end
Now open console or any where you need,
student = Student.find(201410204)
student.full_name
thats it, you will get the full name.
2) Using Scalability of rails, even can execute SQL queries.
student = ActiveRecord::Base.connection.exec_query("SELECT CONCAT(first_name,' ', last_name) FROM students where students.id = 201410204")
It returns an array,now you can retrieve using,
student.rows[0]
Thats it, you will get the same result.

Answer 3

One solution
In model Create A method
def full_name
"#{self.try(:first_name)} #{self.try(:last_name)}"
end
Now
Student.find(121).full_name

Answer 4

With select you restrict the returned columns. Your query returns only the Column Name. id and all other columns are missing. In this case you get an instance of student where all attributes are nil. Only the attribute Name is set. When you try Student.select("concat(first_name, ' ', last_name) as 'Name'").find(201410204).Name you will see the right result.
When you want to get all attributes you have to extend your select like this Student.select("concat(first_name, ' ', last_name) as 'Name', *").find(201410204)
Edit:
I did check it for mysql on https://de.piliapp.com/mysql-syntax-check/, I don't know why but you have to name * first.
Student.select("*, concat(first_name, ' ', last_name) as 'Name'").find(201410204)