SQL - How to find the highest number in a column?

Question

Let\'s say I have the following data in the Customers table: (nothing more)

ID   FirstName   LastName
-------------------------------
20   John        Macken         


        

Answer 1

You can also use relational algebra. A bit lengthy procedure, but here it is just to understand how MAX() works:

E := π_ID (Table_Name)
E1 := π_ID (σ_{ID >= ID'} ((ρ_ID' E) ⋈ E)) – π_ID (σ_{ID < ID’} ((ρ_ID' E) ⋈ E))

Your answer: Table_Name ⋈ E1

Basically what you do is subtract set of ordered relation(a,b) in which a<b from A where a, b ∈ A.

For relation algebra symbols see: Relational algebra From Wikipedia