Re: [PERFORM] Simply join in PostrgeSQL takes too long

[Atesz]

Hi,

You can try some variation:

SELECT 
  book_id
FROM  
  bookgenres, genre_children
WHERE
   bookgenres.genre_id = genre_children.genre_child_id AND  
   genre_children.genre_id = 1
GROUP BY book_id
LIMIT 10

The next works if the 'genre_child_id' is UNIQUE on the 'genre_children'
table.

SELECT 
  book_id
FROM  
  bookgenres
WHERE
   bookgenres.genre_id = (SELECT genre_child_id FROM genre_children
WHERE genre_id = 1)
GROUP BY book_id
LIMIT 10

You may need some index. Try these with EXPLAIN!
CREATE INDEX bookgenres_genre_id_book_id ON bookgenres(genre_id,
book_id);  or
CREATE INDEX bookgenres_book_id_genre_id ON bookgenres(book_id,
genre_id);
CREATE INDEX genre_children_genre_id ON genre_children(genre_id);

Regards, Antal Attila



---------------------------(end of broadcast)---------------------------
TIP 9: the planner will ignore your desire to choose an index scan if your
      joining column's datatypes do not match