On 10/21/19 6:39 AM, Alexander Farber wrote:
Hello, good afternoon!
With PostgreSQL 10 I host a word game, which stores player moves as a
JSON array of objects with properties: col, row, value, letter -
CREATE TABLE words_moves (
mid BIGSERIAL PRIMARY KEY,
action text NOT NULL,
gid integer NOT NULL REFERENCES words_games ON DELETE CASCADE,
uid integer NOT NULL REFERENCES words_users ON DELETE CASCADE,
played timestamptz NOT NULL,
tiles jsonb,
letters text,
hand text,
score integer CHECK(score >= 0),
puzzle boolean NOT NULL DEFAULT false
);
I am trying to construct a query, which would draw a game board when
given a move id (aka mid):
SELECT
hand,
JSONB_ARRAY_ELEMENTS(tiles)->'col' AS col,
JSONB_ARRAY_ELEMENTS(tiles)->'row' AS row,
JSONB_ARRAY_ELEMENTS(tiles)->'letter' AS letter,
JSONB_ARRAY_ELEMENTS(tiles)->'value' AS value
FROM words_moves
WHERE action = 'play' AND
gid = (SELECT gid FROM words_moves WHERE mid = 391416)
AND played <= (SELECT played FROM words_moves WHERE WHERE mid = 391416)
ORDER BY played DESC
The above query works for me and fetches all moves performed in a game
id (aka gid) up to the move id 391416.
In my Java program I then just draw the tiles at the board, one by one
(here a picture: https://slova.de/game-62662/ )
I have however 3 questions please:
1. Is it okay to call JSONB_ARRAY_ELEMENTS four times in the query, will
PostgreSQL optimize that to a single call?
What is the structure of the JSON in tiles?
In other words could you expand the data in one go using jsonb_to_record()?
2. Do you think if it is okay to sort by played timestamp or should I
better sort by mid?
3. Performancewise is it okay to use the 2 subqueries for finding gid
and played when given a mid?
I could see collapsing them into a single query: Something like:
FROM
words_moves
JOIN
(select gid, played from word_moves where mid = 39146) AS m_id
ON
word_moves.gid = m_id.gid
WHERE
...
Thank you
Alex
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
