The field exists only in dotable_a, not in dotable_b

[viki1967]

your english is fine

your sql skills are terrible, and you do not seem to be able to learn

i am not helping you any more, sorry

I wrong with you?
I have asked you run this query

select zn, zn=2 as wtf from dotable_a

and show results in the post #22.
Apologize if I wrong with you... I'm sorry.

[Dan Grossman]

The point of that exercise was to make obvious why you don't want to "select zn=2". That you don't attempt to interpret the results at all means you aren't trying to learn.

[viki1967]

I understand, this query:

select zn, zn=2 as wtf from dotable_a

is wrong... because wtf is 0...