Generated columns using aggregate functions

Question

The starting point

Suppose I have a table devTest that looks like this:

+----+------+  
| id | j    |  
+----+------+  
|  1 |    5 |  
|          


        

Answer 1

This error makes sense because any change in your table (say you add a j with value 0) would update your average, and this in turn would change all your generated columns. So this would be quite a bit of work for the query engine.

Another solution would be to define a view instead:

CREATE VIEW j_dev (id, j, j_dev) AS 
SELECT id, j, 
       (j - avg(j)) / std(j) as j_dev
FROM devTest

(not sure about the create view syntax, correct me if I'm wrong)