Please let me rephrase my question so that it is better understandable - In PostgreSQL 9.5.3 I keep player infos from various social networks:
# TABLE words_social; sid | social | female | given | family | photo | place | stamp | uid -------+--------+--------+---------+--------+-------+-------+------------+----- aaaaa | 1 | 0 | Abcde1 | | | | 1470237061 | 1 aaaaa | 2 | 0 | Abcde2 | | | | 1477053188 | 1 aaaaa | 3 | 0 | Abcde3 | | | | 1477053330 | 1 kkkkk | 3 | 0 | Klmnop3 | | | | 1477053810 | 2 kkkkk | 4 | 0 | Klmnop4 | | | | 1477053857 | 2 ggggg | 2 | 0 | Ghijk2 | | | | 1477053456 | 3 ggggg | 3 | 0 | Ghijk3 | | | | 1477053645 | 3 ggggg | 4 | 0 | Ghijk4 | | | | 1477053670 | 3 xxxxx | 4 | 0 | Xyzok | | | | 1470237393 | 4 (9 rows) The 1,2,3,4 in column "social" means "Facebook", "Twitter", etc. For a player I can always select her "most recent" info by: # select * from words_social s1 WHERE stamp = (SELECT max(stamp) FROM words_social s2 WHERE s1.uid = s2.uid); sid | social | female | given | family | photo | place | stamp | uid -------+--------+--------+---------+--------+-------+-------+------------+----- aaaaa | 3 | 0 | Abcde3 | | | | 1477053330 | 1 kkkkk | 4 | 0 | Klmnop4 | | | | 1477053857 | 2 ggggg | 4 | 0 | Ghijk4 | | | | 1477053670 | 3 xxxxx | 4 | 0 | Xyzok | | | | 1470237393 | 4 (4 rows) Then there is another table storing current games (I have omitted some columns with game data below): # select gid, created, finished, player1, player2 from words_games; gid | created | finished | player1 | player2 -----+-------------------------------+----------+---------+--------- 1 | 2016-10-21 14:51:12.624507+02 | | 4 | 1 2 | 2016-10-21 14:51:22.631507+02 | | 3 | (2 rows) Whenever a user (for example with uid=1) connects to the server, I send her the games she is taking part in: # select gid, created, finished, player1, player2 from words_games where player1=1 union select gid, created, finished, player2, player1 from words_games where player2=1; gid | created | finished | player1 | player2 -----+-------------------------------+----------+---------+--------- 1 | 2016-10-21 14:51:12.624507+02 | | 4 | 1 (1 row) My problem: to the above UNION SELECT statement I need to add user infos from words_social table. (So that I can display user photos and names above the game board) So I try this with CTE: # with user_infos AS (select * from words_social s1 WHERE stamp = (SELECT max(stamp) FROM words_social s2 WHERE s1.uid = s2.uid)) select g.gid, g.created, g.finished, g.player1, g.player2, i.given from words_games g join user_infos i on (g.player1=i.uid) where g.player1=1 union select g.gid, g.created, g.finished, g.player2, g.player1, i.given from words_games g join user_infos i on (g.player2=i.uid) where g.player2=1; gid | created | finished | player1 | player2 | given -----+-------------------------------+----------+---------+---------+-------- 1 | 2016-10-21 14:51:12.624507+02 | | 1 | 4 | Abcde3 (1 row) This works well (I have advanced since me first asking few days ago), but I still have the following problem - I am worried that the CTE-table user_infos will get very large, once my game has many players. How to rewrite my query, so that I fetch games and users (player1, player2) for a certain user id (uid) - without making huge intermediate tables? Thank you Alex
