Hi all

The test data and sql is in the following mail.


After I disabled hash join and nested-loop join(set enable_hashjoin = off; set 
enable_nestloop = off;) and execute the query again,the query plan changes to 
the following one .

"Merge Join  (cost=3179.24..3183.55 rows=200 width=1044) (actual 
time=2.409..8.969 rows=9999 loops=1)"
"  Merge Cond: (als.node_no = l1.level1_no)"
"  ->  Merge Join  (cost=3168.59..3249.95 rows=200 width=528) (actual 
time=2.362..5.933 rows=9999 loops=1)"
"        Merge Cond: (als.node_no = l2.parent_no)"
"        ->  Index Scan using all_level_status_pkey on all_level_status als  
(cost=0.29..109.10 rows=200 width=4) (actual time=0.023..0.152 rows=200 
"              Index Cond: (level = 1)"
"              Filter: (status = 0)"
"        ->  Materialize  (cost=3168.30..3218.30 rows=9999 width=524) (actual 
time=2.334..3.888 rows=9999 loops=1)"
"              ->  Sort  (cost=3168.30..3193.30 rows=9999 width=524) (actual 
time=2.330..2.778 rows=9999 loops=1)"
"                    Sort Key: l2.parent_no"
"                    Sort Method: quicksort  Memory: 853kB"
"                    ->  Seq Scan on level2_table l2  (cost=0.00..144.99 
rows=9999 width=524) (actual time=0.007..0.924 rows=9999 loops=1)"
"  ->  Sort  (cost=10.64..11.14 rows=200 width=520) (actual time=0.045..0.561 
rows=9950 loops=1)"
"        Sort Key: l1.level1_no"
"        Sort Method: quicksort  Memory: 34kB"
"        ->  Seq Scan on level1_table l1  (cost=0.00..3.00 rows=200 width=520) 
(actual time=0.006..0.016 rows=200 loops=1)"
"Planning time: 1.379 ms"
"Execution time: 9.422 ms"

The actual rows(rows=9950) part in the following line contained in the above 
query plan seems strange.
"  ->  Sort  (cost=10.64..11.14 rows=200 width=520) (actual time=0.045..0.561 
rows=9950 loops=1)"
Shouldn't it be 200?


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