calculate a field in mysql table

Question

I am very new to MySQL and db's in general.

I have a table where I have date_of_test and test_frequency (Possible values 3,6,12).

I need to have a field future_test that has the calculated date in it derived from date_of_test and the value in test_frequency which is either 3,6,12 (Months).

I do not know how to achieve this, could somebody point me in the right direction?

Answer 1

try DATE_ADD() function in my sql

ex:

 SELECT '2008-12-31 23:59:59' + INTERVAL 1 MONTH

Answer 2

alter table gypsum add column future_test (datetime);

update gypsum
  set future_test = date_add(date_of_test, interval test_frequency MONTH);

As pointed in comments, it's often not a great idea to have calculated values in a database.

You'll have to relaunch the calculation each time you update a date_or_test, a test_frequency, or each time you insert a new value...

It might be better to create a dedicated view

CREATE OR REPLACE VIEW gypsumWithFuture AS
(SELECT
  id, 
  date_of_test, 
  test_frequency, 
  DATE_ADD(date_of_test, interval test_frequency MONTH) AS future_test
 FROM gypsum)

or to do the calculation in your application's code (if you have one). A wide range of langagues has DateTime function, which can do the same as MySQL DATE_ADD .