ruby-on-rails – Active Record的’join’方法背后有什么？

"Game.joins(:round).where('rounds.league_id = 1')"

和

"Game.joins(:round).where(:rounds => {:league_id => 1})"

第一个产生查询：

Game Load (7.5ms) 
SELECT "games".* 
FROM "games" INNER JOIN "rounds" ON "rounds"."id" = "games"."round_id" 
WHERE (rounds.league_id = 1)

而第二个产生较长的一个：

SQL (1.7ms) 
    SELECT a.attname,format_type(a.atttypid,a.atttypmod),d.adsrc,a.attnotnull
    FROM pg_attribute a LEFT JOIN pg_attrdef d
    ON a.attrelid = d.adrelid AND a.attnum = d.adnum
    WHERE a.attrelid = '"rounds"'::regclass
    AND a.attnum > 0 AND NOT a.attisdropped
    ORDER BY a.attnum

Game Load (8.8ms) 
    SELECT "games".* 
    FROM "games" 
    INNER JOIN "rounds" ON "rounds"."id" = "games"."round_id" 
    WHERE "rounds"."league_id" = 1

先谢谢大家,我刚加入社区,这是我的第一个问题