Question :
There might be a really obvious solution to my question, but I am stuck and did not manage find out what I am doing wrong, so you guys might tell me.
I am not able to create a nullable stored column for my expression using the DATE_ADD function in MySQL 8.
See the following example:
ADD COLUMN `test` TIMESTAMP GENERATED ALWAYS AS (DATE_ADD(col1, INTERVAL col2 HOUR)) STORED NULL;
col1 is TIMESTAMP and col2 is INT
MySQL does not complain, but just converts the expression to
(`col1` + interval `col2` hour)
And the resulting is not nullable as well.
Answer :
Mysql has done, what you ask of him.
here are more infomration
DATE_ADD(col1, INTERVAL col2 HOUR) is equal to (col1 + interval col2 hour)
And is set as Default Value for the column. so when you add a NULL you get what ever (col1 + interval col2 hour) represents.
So you can’t achieve a Nullable and generated Column at the same time.
If You need A NULL there, you have to generate the test column VALUE at runtime.