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Re: Forward declaration of table - Mailing list pgsql-general

From Igor Neyman
Subject Re: Forward declaration of table
Date
Msg-id MWHPR07MB2877A4811B306B5DE275F791DAEB0@MWHPR07MB2877.namprd07.prod.outlook.com
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In response to Re: Forward declaration of table  (Alexander Farber <alexander.farber@gmail.com>)
Responses Re: Forward declaration of table  (Alexander Farber <alexander.farber@gmail.com>)
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From: pgsql-general-owner@postgresql.org [mailto:pgsql-general-owner@postgresql.org] On Behalf Of Alexander Farber
Sent: Tuesday, August 23, 2016 3:33 PM
Cc: pgsql-general <pgsql-general@postgresql.org>
Subject: Re: [GENERAL] Forward declaration of table

 

Hi Igor,

 

On Tue, Aug 23, 2016 at 8:15 PM, Igor Neyman <ineyman@perceptron.com> wrote:

mailto:pgsql-general-owner@postgresql.org] On Behalf Of Alexander Farber 

Certain MOVE exists only within particular GAME: no GAME -> no MOVE (on delete cascade).

So, you don’t need mid1, mid2 columns in WORD_GAMES table.

What you need is this column in WORD_MOVES table:

 

gid integer REFERENCES WORD_GAMES ON DELETE CASCADE

 

 

you are correct, but I need to send most recent move in each game together with the other game data.

If I don't store the recent moves in mid1, mid2 then I'd have to retrieve them every time dynamically with 

WITH last_moves AS (

  SELECT *

  FROM words_moves wm1

  WHERE

    played = (SELECT max(played)

              FROM words_moves wm2

              WHERE wm1.gid = wm2.gid))

SELECT *

FROM words_games wg

  LEFT JOIN last_moves lm

    ON (wg.gid = lm.gid)

WHERE

  player1 = 1 OR

  player2 = 1;

 

Regards

Alex

 

Or, for the last moves you could probably have the third table LAST_MOVES maintained through triggers on WORDS_MOVES table.

Then, you just join WORDS_GAMES and LAST_MOVES tables.

 

Regards,

Igor

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