为什么postgresql中的视图不使用索引？
我有一个大表（星表目录），其中有一个子集。我实现了子集 作为两个表的并集，我使用交叉索引 问题是来自视图的查询似乎没有使用索引，所用的时间与扫描表所用的时间相同 对大表的查询会快速进行：为什么postgresql中的视图不使用索引？,postgresql,view,indexing,Postgresql,View,Indexing,我有一个大表（星表目录），其中有一个子集。我实现了子集 作为两个表的并集，我使用交叉索引 问题是来自视图的查询似乎没有使用索引，所用的时间与扫描表所用的时间相同 对大表的查询会快速进行： select count(*) from ucac4 where rnm in (select ucac4_rnm from grid_catalog limit 5); count ------- 5 (1 row) Time: 12.132 ms 对视图的查询不会很快进行，即使我希望它会进行
select count(*) from ucac4 where rnm in (select ucac4_rnm from grid_catalog limit 5);
count
-------
5
(1 row)
Time: 12.132 ms
select count(*) from grid_catalog_view where ident in (select ucac4_rnm from grid_catalog limit 5);
count
-------
5
(1 row)
Time: 1056237.045 ms
Aggregate (cost=23175810.51..23175810.52 rows=1 width=0)
-> Hash Join (cost=23081888.41..23172893.67 rows=1166734 width=0)
Hash Cond: (ucac4.rnm = public.grid_catalog.ucac4_rnm)
-> Unique (cost=23081888.17..23140224.87 rows=2333468 width=44)
-> Sort (cost=23081888.17..23087721.84 rows=2333468 width=44)
Sort Key: ucac4.ra, ucac4."dec", ucac4.pmrac, ucac4.pmdc, ucac4.rnm, ucac4.nest4, ucac4.nest6, ucac4.nest7, public.grid_catalog.subset
-> Append (cost=63349.87..22763295.24 rows=2333468 width=44)
-> Hash Join (cost=63349.87..22738772.75 rows=2333467 width=44)
Hash Cond: (ucac4.rnm = public.grid_catalog.ucac4_rnm)
-> Seq Scan on ucac4 (cost=0.00..16394129.04 rows=455124304 width=40)
-> Hash (cost=34048.69..34048.69 rows=2344094 width=8)
-> Seq Scan on grid_catalog (cost=0.00..34048.69 rows=2344094 width=8)
Filter: (petrov_prikey IS NULL)
-> Hash Join (cost=415.51..1187.80 rows=1 width=36)
Hash Cond: (petrov.prikey = public.grid_catalog.petrov_prikey)
-> Seq Scan on petrov (cost=0.00..709.15 rows=7215 width=32)
-> Hash (cost=282.08..282.08 rows=10675 width=8)
-> Index Scan using grid_catalog_petrov_prikey_idx on grid_catalog (cost=0.00..282.08 row
s=10675 width=8)
-> Hash (cost=0.18..0.18 rows=5 width=4)
-> HashAggregate (cost=0.13..0.18 rows=5 width=4)
-> Limit (cost=0.00..0.07 rows=5 width=4)
-> Seq Scan on grid_catalog (cost=0.00..34048.69 rows=2354769 width=4)
(22 rows)
select count(*) from grid_catalog_view;
count
---------
1597359
(1 row)
Time: 1033732.786 ms
PS1=# \d grid_catalog_view
View "public.grid_catalog_view"
Column | Type | Modifiers
--------+------------------+-----------
ra | double precision |
dec | double precision |
pmrac | integer |
pmdc | integer |
ident | integer |
nest4 | integer |
nest6 | integer |
nest7 | integer |
subset | integer |
View definition:
SELECT ucac4.ra, ucac4."dec", ucac4.pmrac, ucac4.pmdc, ucac4.rnm AS ident, ucac4.nest4, ucac4.nest6, ucac4.nest7, grid_catalog.subset
FROM ucac4, grid_catalog
WHERE ucac4.rnm = grid_catalog.ucac4_rnm AND grid_catalog.petrov_prikey IS NULL
UNION
SELECT petrov.ra, petrov."dec", 0 AS pmrac, 0 AS pmdc, grid_catalog.petrov_prikey AS ident, petrov.nest4, petrov.nest6, petrov.nest7, grid_catalog.subset
FROM petrov, grid_catalog
WHERE petrov.prikey = grid_catalog.petrov_prikey AND grid_catalog.ucac4_rnm IS NULL;
PS1=# \d ucac4
Table "public.ucac4"
Column | Type | Modifiers
----------+------------------+-----------
radi | bigint |
spdi | bigint |
magm | smallint |
maga | smallint |
sigmag | smallint |
objt | smallint |
cdf | smallint |
... deleted entries not of relavance ...
ra | double precision |
dec | double precision |
x | double precision |
y | double precision |
z | double precision |
nest4 | integer |
nest6 | integer |
nest7 | integer |
Indexes:
"ucac4_pkey" PRIMARY KEY, btree (rnm)
"q3c_ucac4_idx" btree (q3c_ang2ipix(ra, "dec")) CLUSTER
"ucac4_nest4_idx" btree (nest4)
"ucac4_nest6_idx" btree (nest6)
"ucac4_nest7_idx" btree (nest7)
Referenced by:
TABLE "grid_catalog" CONSTRAINT "grid_catalog_ucac4_rnm_fkey" FOREIGN KEY (ucac4_rnm) REFERENCES ucac4(rnm)
PS1=# \d grid_catalog_view
View "public.grid_catalog_view"
Column | Type | Modifiers
--------+------------------+-----------
ra | double precision |
dec | double precision |
pmrac | integer |
pmdc | integer |
ident | integer |
nest4 | integer |
nest6 | integer |
nest7 | integer |
subset | integer |
View definition:
SELECT ucac4.ra, ucac4."dec", ucac4.pmrac, ucac4.pmdc, ucac4.rnm AS ident, ucac4.nest4, ucac4.nest6, ucac4.nest7, grid_catalog.subset
FROM ucac4, grid_catalog
WHERE ucac4.rnm = grid_catalog.ucac4_rnm AND grid_catalog.petrov_prikey IS NULL
UNION
SELECT petrov.ra, petrov."dec", 0 AS pmrac, 0 AS pmdc, grid_catalog.petrov_prikey AS ident, petrov.nest4, petrov.nest6, petrov.nest7, grid_catalog.subset
FROM petrov, grid_catalog
WHERE petrov.prikey = grid_catalog.petrov_prikey AND grid_catalog.ucac4_rnm IS NULL;
PS1=# \d ucac4
Table "public.ucac4"
Column | Type | Modifiers
----------+------------------+-----------
radi | bigint |
spdi | bigint |
magm | smallint |
maga | smallint |
sigmag | smallint |
objt | smallint |
cdf | smallint |
... deleted entries not of relavance ...
ra | double precision |
dec | double precision |
x | double precision |
y | double precision |
z | double precision |
nest4 | integer |
nest6 | integer |
nest7 | integer |
Indexes:
"ucac4_pkey" PRIMARY KEY, btree (rnm)
"q3c_ucac4_idx" btree (q3c_ang2ipix(ra, "dec")) CLUSTER
"ucac4_nest4_idx" btree (nest4)
"ucac4_nest6_idx" btree (nest6)
"ucac4_nest7_idx" btree (nest7)
Referenced by:
TABLE "grid_catalog" CONSTRAINT "grid_catalog_ucac4_rnm_fkey" FOREIGN KEY (ucac4_rnm) REFERENCES ucac4(rnm)
知道为什么我的索引没有被使用吗？据我所知，这是postgres的一个限制-很难避免以这种方式扫描工会上的整个表格 见： 及 也可能是相关的
基本上-我想您需要重新访问视图定义！抱歉，没有确定的解决方案。什么索引？我没有看到任何索引的定义。我忘了包括表架构。修复。
解释分析