I see, thank you for your comments, David and Adrian.
In the "tiles" column actually save either the JSON array of tiles - when the user plays them
Or a string (which is jsonb too) concatenated of letters - when the user swaps the letters.
Maybe I should rethink my table structure (I just want to "log" all plays, swaps, skips, resigns in the words_moves table)...
Or maybe I should always check for the "action" column first (acts as enum) - before accessing "tiles" column....
A table constraint like:
CASE WHEN action = 'Play'
THEN lengh < 0
WHEN action = 'Swap'
THEN ...
ELSE false
END
Is perfectly fine - though having actual non-null values take on different meanings based upon the enum is generally not a good idea. I've been using the above to enforce conditional not null constraints when I don't want to implement explicit inheritance.
