小编Dor*_* W.的帖子

我的查询是：

SELECT  Acol1, Acol2, Bcol1, Bcol2, Ccol1, Ccol2
FROM    tableA LEFT JOIN
            (tableB FULL JOIN tableC ON (Bcol1 = Ccol1))
            ON (Acol1 = Bcol1)

EXPLAIN ANALYZE给我：

                                                      QUERY PLAN                                                      
----------------------------------------------------------------------------------------------------------------------
 Hash Right Join  (cost=99.65..180.45 rows=1770 width=24) (actual time=0.043..0.103 rows=3 loops=1)
   Hash Cond: (tableb.bcol1 = tablea.acol1)
   ->  Hash Left Join  (cost=49.83..104.08 rows=1770 width=16) (actual time=0.011..0.062 rows=3 loops=1)
         Hash Cond: (tableb.bcol1 = tablec.ccol1)
         ->  Seq Scan on tableb  (cost=0.00..27.70 rows=1770 width=8) (actual time=0.001..0.002 rows=3 loops=1)
         ->  Hash  (cost=27.70..27.70 rows=1770 width=8) (actual time=0.004..0.004 …