从执行计划来看，IN版本比EXISTS版本
更快我认为EXISTS查询更快，因为急切地检查条件。 IN查询虽然看起来很直观，但我觉得它似乎很晚就解决了最终条件的结果;也就是说，从内到外，我认为IN较慢，因为下一个条件需要等待以获得其内在条件的结果。
虽然从下面的执行计划来看，IN更快;它的成本较低。
我的一部分想要使用IN版本，对于下一个维护者来说，它看起来简单直观，下面的执行计划似乎表明它比EXISTS更快。但我的另一部分是想要使用EXISTS，因为我觉得它更快，但下面的执行计划似乎与这种看法相矛盾。
以下两个查询中的哪一个更快，是IN版本还是EXISTS版本？
IN版本：
explain analyze
select ceil(
( count(distinct company_rec_id)::numeric + 1 )
/ ((1)) )::int
from
parcel ord
join company c on c.company_rec_id = ord.client_rec_id
where
(
(((E'')) <> '' and to_tsvector(c.company) @@ plainto_tsquery(extract_words(((E'')))))
or ((E'')) = ''
)
and
(
(((0)) <> 0 and ord.parcel_number = ((0)))
or ((0)) = 0
)
and parcel_rec_id in
(
select parcel_rec_id
from parcel_application
where parcel_application_rec_id in
(
select parcel_application_rec_id
from parcel_application_shoe
where
(
(((E'')) <> '' and to_tsvector(extract_words(shoe_description)) @@ plainto_tsquery(extract_words(((E'')))))
or ((E'')) = ''
)
and
(
(((E'')) <> '' and to_tsvector(extract_words(order_number)) @@ plainto_tsquery(extract_words(((E'')))))
or ((E'')) = ''
)
and
(
(((E'')) <> '' and to_tsvector(extract_words(style_number)) @@ plainto_tsquery(extract_words(((E'')))))
or ((E'')) = ''
)
)
)
"Aggregate (cost=1060.73..1060.75 rows=1 width=37) (actual time=29.028..29.028 rows=1 loops=1)"
" -> Hash Join (cost=880.43..1053.04 rows=3074 width=37) (actual time=13.261..16.365 rows=3074 loops=1)"
" Hash Cond: ((ord.client_rec_id)::text = (c.company_rec_id)::text)"
" -> Hash Join (cost=864.79..995.14 rows=3074 width=37) (actual time=13.115..15.027 rows=3074 loops=1)"
" Hash Cond: ((ord.parcel_rec_id)::text = (parcel_application.parcel_rec_id)::text)"
" -> Seq Scan on parcel ord (cost=0.00..78.87 rows=3087 width=74) (actual time=0.005..0.373 rows=3087 loops=1)"
" -> Hash (cost=826.37..826.37 rows=3074 width=37) (actual time=13.102..13.102 rows=3074 loops=1)"
" -> HashAggregate (cost=795.63..826.37 rows=3074 width=37) (actual time=11.835..12.281 rows=3074 loops=1)"
" -> Hash Join (cost=541.34..787.59 rows=3218 width=37) (actual time=7.076..10.286 rows=3218 loops=1)"
" Hash Cond: ((parcel_application.parcel_application_rec_id)::text = (parcel_application_shoe.parcel_application_rec_id)::text)"
" -> Seq Scan on parcel_application (cost=0.00..122.18 rows=3218 width=74) (actual time=0.004..0.710 rows=3218 loops=1)"
" -> Hash (cost=501.12..501.12 rows=3218 width=37) (actual time=7.061..7.061 rows=3218 loops=1)"
" -> HashAggregate (cost=468.94..501.12 rows=3218 width=37) (actual time=5.721..6.220 rows=3218 loops=1)"
" -> Seq Scan on parcel_application_shoe (cost=0.00..442.95 rows=10395 width=37) (actual time=0.004..2.318 rows=10395 loops=1)"
" -> Hash (cost=11.95..11.95 rows=295 width=37) (actual time=0.136..0.136 rows=295 loops=1)"
" -> Seq Scan on company c (cost=0.00..11.95 rows=295 width=37) (actual time=0.013..0.068 rows=295 loops=1)"
"Total runtime: 29.122 ms"
EXISTS版本：
explain analyze
select ceil(
( count(distinct company_rec_id)::numeric + 1 )
/ ((1)) )::int from
parcel ord
join company c on c.company_rec_id = ord.client_rec_id
where
(
(((E'')) <> '' and to_tsvector(c.company) @@ plainto_tsquery(extract_words(((E'')))))
or ((E'')) = ''
)
and
(
(((0)) <> 0 and ord.parcel_number = ((0)))
or ((0)) = 0
)
and exists
(
select * from parcel_application pa
where pa.parcel_rec_id = ord.parcel_rec_id
and
exists
(
select * from parcel_application_shoe ord_item
where
ord_item.parcel_application_rec_id = pa.parcel_application_rec_id
and
(
(((E'')) <> '' and to_tsvector(extract_words(ord_item.shoe_description)) @@ plainto_tsquery(extract_words(((E'')))))
or ((E'')) = ''
)
and
(
(((E'')) <> '' and to_tsvector(extract_words(ord_item.order_number)) @@ plainto_tsquery(extract_words(((E'')))))
or ((E'')) = ''
)
and
(
(((E'')) <> '' and to_tsvector(extract_words(ord_item.style_number)) @@ plainto_tsquery(extract_words(((E'')))))
or ((E'')) = ''
)
)
)
"Aggregate (cost=17773.13..17773.16 rows=1 width=37) (actual time=34.519..34.520 rows=1 loops=1)"
" -> Hash Join (cost=17636.59..17769.11 rows=1609 width=37) (actual time=17.174..20.426 rows=3074 loops=1)"
" Hash Cond: ((ord.client_rec_id)::text = (c.company_rec_id)::text)"
" -> Hash Join (cost=17620.95..17731.35 rows=1609 width=37) (actual time=16.882..18.862 rows=3074 loops=1)"
" Hash Cond: ((ord.parcel_rec_id)::text = (pa.parcel_rec_id)::text)"
" -> Seq Scan on parcel ord (cost=0.00..78.87 rows=3087 width=74) (actual time=0.006..0.409 rows=3087 loops=1)"
" -> Hash (cost=17601.74..17601.74 rows=1537 width=37) (actual time=16.858..16.858 rows=3074 loops=1)"
" -> HashAggregate (cost=17586.37..17601.74 rows=1537 width=37) (actual time=15.015..15.535 rows=3074 loops=1)"
" -> Seq Scan on parcel_application pa (cost=0.00..17582.35 rows=1609 width=37) (actual time=10.040..12.440 rows=3218 loops=1)"
" Filter: (alternatives: SubPlan 1 or hashed SubPlan 2)"
" SubPlan 1"
" -> Index Scan using fki_parcel_application_shoe__parcel_application on parcel_application_shoe ord_item (cost=0.00..16.28 rows=3 width=0) (never executed)"
" Index Cond: ((parcel_application_rec_id)::text = ($0)::text)"
" SubPlan 2"
" -> Seq Scan on parcel_application_shoe ord_item (cost=0.00..442.95 rows=10395 width=37) (actual time=0.005..4.482 rows=10395 loops=1)"
" -> Hash (cost=11.95..11.95 rows=295 width=37) (actual time=0.284..0.284 rows=295 loops=1)"
" -> Seq Scan on company c (cost=0.00..11.95 rows=295 width=37) (actual time=0.010..0.155 rows=295 loops=1)"
"Total runtime: 34.645 ms"
这是我最终使用的最终查询， IN 版本。我只能感觉到边际性能差异 IN和EXISTS版本。我正在考虑下一个维护者的可读性，因此我使用 IN
select ord.parcel_number, ord.received_date, c.company
from parcel ord
join company c on c.company_rec_id = ord.client_rec_id
where
(
:_company = ''
or
to_tsvector(c.company) @@ plainto_tsquery(extract_words(:_company))
)
and
(
:_fttsc_num = 0
or ord.parcel_number = :_fttsc_num
)
and
(
(:_item = '' and :_order_num = '' and :_style_num = '')
or
ord.parcel_rec_id in
(
select parcel_rec_id
from parcel_application
where parcel_application_rec_id in
(
select parcel_application_rec_id
from parcel_application_shoe
where
(
:_item = ''
or to_tsvector(extract_words(shoe_description)) @@ plainto_tsquery(extract_words(:_item))
)
and
(
:_order_num = ''
or to_tsvector(extract_words(order_number)) @@ plainto_tsquery(extract_words(:_order_num))
)
and
(
:_style_num = ''
or to_tsvector(extract_words(style_number)) @@ plainto_tsquery(extract_words(:_style_num))
)
) -- parcel_application_rec_id IN
) -- parcel_rec_id IN
)
and
-- material filter...
(
(:_material = '')
or
-- implied material <> ''
parcel_rec_id in
(
select parcel_rec_id
from parcel_application
where parcel_application_rec_id in
(
select parcel_application_rec_id
from mlist
where mlist_rec_id in
(
select mlist_rec_id
from mlist_detail
join material m using(material_rec_id)
where to_tsvector(extract_words(m.material)) @@ plainto_tsquery(extract_words(:_material))
)
)
)
)
-- ...material filter
and
-- parameter filter...
(
(:_parameter = '')
or
-- implied parameter <> ''
parcel_rec_id in
(
select parcel_rec_id
from parcel_application
where parcel_application_rec_id in
(
select parcel_application_rec_id
from mlist
where mlist_rec_id in
(
select mlist_rec_id
from mlist_detail
where mlist_detail_rec_id in
(
select mlist_detail_rec_id
from mlist_detail_parameter
join parameter p using(parameter_rec_id)
where to_tsvector(extract_words(p.parameter)) @@ plainto_tsquery(extract_words(:_parameter))
)
)
)
)
)
-- ...parameter filter
order by ord.received_date
答案 0 :(得分：1)
您可能想要重新检查嵌套的EXISTS（）子查询集。 In the past似乎使用它们的效果不如在内连接上使用单个EXISTS那么好。
所以一般来说，转换如下：
where exists (select 1 from foo where foo.outer_id = outer.outer_id
and exists (select 1 from bar where bar.foo_id = foo.foo_id))
到
where exists (select 1 from foo join bar using (foo_id)
where foo.outer_id = outer.outer_id)