How to make the field get the value automatically?

Question

SQL Server

There is a db list of athletes in it, it is necessary to calculate his category, that is, if his age is between 0-15 years old, then category C, if between 15 and 17, then category A. All this is necessary to generate automotility based on age (if an athlete’s age has changed, then category too). Through php it's all easy but I need to do it through sql.
I found commands under sql server but they have a different syntax.

alter table PATIENT add AgeCategory as
    CASE
    WHEN DateAdd(Year,1,DOB) > Current_Timestamp then 'infant'
    WHEN DateAdd(Year,4,DOB) > Current_Timestamp then 'toddler'
    WHEN DateAdd(Year,10,DOB) > Current_Timestamp then 'children'
    WHEN DateAdd(Year,14,DOB) > Current_Timestamp then 'tween'
    WHEN DateAdd(Year,18,DOB) > Current_Timestamp then 'teenager'
    WHEN DateAdd(Year,65,DOB) > Current_Timestamp then 'adult'
    ELSE 'elderly'
    END;

Answer 1

Use a trigger before adding an entry, or a default value from a function.

Answer 2

So what's the question? It is perfectly normal for SQL to add a calculated field
to the table , as shown in the example.

Answer 3

Everything was decided through cross join