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....