这 EXPLAIN 是否表明为什么 Postgres 查询如此缓慢
Does this EXPLAIN indicate why Postgres query so slow
我在 Postgres SQL 数据库上执行了一些查询，大多数查询执行得非常快，但有一个执行得非常慢。即使在测试时我只限制主版本 table 的 100 条记录（所有查询都基于版本 table），它也需要 50 秒 ，而所有其他查询都不到一秒
这是键table，其中包含多行
l_artist_recording
Column | Type | Modifiers
----------------+--------------------------+-----------------------------------------------------------------
id | integer | not null default nextval('l_artist_recording_id_seq'::regclass)
link | integer | not null
entity0 | integer | not null
entity1 | integer | not null
edits_pending | integer | not null default 0
last_updated | timestamp with time zone | default now()
link_order | integer | not null default 0
entity0_credit | text | not null default ''::text
entity1_credit | text | not null default ''::text
Indexes:
"l_artist_recording_pkey" PRIMARY KEY, btree (id)
"l_artist_recording_idx_uniq" UNIQUE, btree (entity0, entity1, link, link_order)
"l_artist_recording_entity1_idx" btree (entity1)
"l_artist_recording_idx_entity1" btree (entity1)
"l_artist_recording_link" btree (link)
Check constraints:
"l_artist_recording_edits_pending_check" CHECK (edits_pending >= 0)
"l_artist_recording_link_order_check" CHECK (link_order >= 0)
recording_release
Table "musicbrainz.recording_release"
Column | Type | Modifiers
--------------+---------+-----------
recording_id | integer | not null
release_id | integer | not null
Indexes:
"recording_release_pkey" PRIMARY KEY, btree (recording_id, release_id)
"recording_release_recording_id" btree (recording_id)
"recording_release_release_id" btree (release_id)
艺术家
Column | Type | Modifiers
------------------+--------------------------+-----------------------------------------------------
id | integer | not null default nextval('artist_id_seq'::regclass)
gid | uuid | not null
name | character varying | not null
sort_name | character varying | not null
begin_date_year | smallint |
begin_date_month | smallint |
begin_date_day | smallint |
end_date_year | smallint |
end_date_month | smallint |
end_date_day | smallint |
type | integer |
area | integer |
gender | integer |
comment | character varying(255) | not null default ''::character varying
edits_pending | integer | not null default 0
last_updated | timestamp with time zone | default now()
ended | boolean | not null default false
begin_area | integer |
end_area | integer |
Indexes:
"artist_pkey" PRIMARY KEY, btree (id)
"artist_idx_gid" UNIQUE, btree (gid)
"artist_idx_area" btree (area)
"artist_idx_begin_area" btree (begin_area)
"artist_idx_end_area" btree (end_area)
"artist_idx_lower_name" btree (lower(name::text))
"artist_idx_name" btree (name)
"artist_idx_sort_name" btree (sort_name)
Check constraints:
"artist_edits_pending_check" CHECK (edits_pending >= 0)
"artist_ended_check" CHECK ((end_date_year IS NOT NULL OR end_date_month IS NOT NULL OR end_date_day IS NOT NULL) AND ended = true OR end_date_year IS NULL AND end_date_month IS NULL AND end_date_day IS NULL)
这是我的查询
SELECT DISTINCT t1.entity1 as recordingId,
t1.entity0 as artistId,
t2.id as linkid,
t3.name as type,
t4.name,
t4.sort_name,
t4.gid,
t9.latinname as latinName,
t9.islatin,
t7.name as linkattribute,
at.name as artistType
FROM l_artist_recording t1
INNER JOIN link t2 on t1.link=t2.id
INNER JOIN link_type t3 on t2.link_type=t3.id
AND (t3.name='performer' OR t3.name='instrument' OR t3.name='vocal' )
LEFT JOIN link_attribute t6
ON t6.link = t2.id
LEFT JOIN link_attribute_type t7
ON t6.attribute_type = t7.id
INNER JOIN artist t4 on t1.entity0=t4.id
INNER JOIN artist_latin t9 on t9.id=t4.id
LEFT JOIN artist_type at on t4.type=at.id
INNER JOIN recording t5 on t1.entity1=t5.id
INNER JOIN recording_release rr ON t5.id = rr.recording_id
WHERE rr.release_id BETWEEN ? AND ?
ORDER BY recordingId, artistId, linkid, linkattribute";
我已经检查了所有 table 以确保它们在要连接的任何字段上都有索引，在少数情况下它丢失了所以我添加了。我也在那些 table 上 运行 VACUUM ANALYZE 但这没有什么区别。
这是我的解释（分析、缓冲）输出
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Unique (cost=336796.42..336797.05 rows=21 width=99) (actual time=93229.472..93233.580 rows=1271 loops=1)
Buffers: shared hit=5215 read=97399, temp read=138990 written=138908
-> Sort (cost=336796.42..336796.48 rows=21 width=99) (actual time=93229.468..93230.653 rows=1286 loops=1)
Sort Key: t1.entity1, t1.entity0, t2.id, t7.name, t3.name, t4.name, t4.sort_name, t4.gid, t9.latinname, t9.islatin, at.name
Sort Method: quicksort Memory: 245kB
Buffers: shared hit=5215 read=97399, temp read=138990 written=138908
-> Nested Loop (cost=334176.87..336795.96 rows=21 width=99) (actual time=91632.892..93226.628 rows=1286 loops=1)
Buffers: shared hit=5197 read=97399, temp read=138990 written=138908
-> Hash Join (cost=334176.44..336665.45 rows=21 width=103) (actual time=91632.830..93211.718 rows=1286 loops=1)
Hash Cond: (rr.recording_id = t1.entity1)
Buffers: shared hit=151 read=97315, temp read=138990 written=138908
-> Index Scan using recording_release_release_id on recording_release rr (cost=0.44..1833.24 rows=891 width=4) (actual time=0.028..2.371 rows=825 loops=1)
Index Cond: ((release_id >= 1) AND (release_id <= 100))
Buffers: shared hit=130 read=121
-> Hash (cost=333485.62..333485.62 rows=55230 width=99) (actual time=91631.881..91631.881 rows=3813157 loops=1)
Buckets: 8192 Batches: 32 (originally 1) Memory Usage: 20481kB
Buffers: shared hit=21 read=97194, temp read=61835 written=116275
-> Hash Left Join (cost=132574.41..333485.62 rows=55230 width=99) (actual time=12380.770..84898.987 rows=3813157 loops=1)
Hash Cond: (t4.type = at.id)
.....
这就是问题的症结所在，我的 EXPLAIN 是否告诉我查询会执行得很糟糕，我无法判断，尽管我确实注意到一些我认为是糟糕的顺序扫描。
为了了解数据库的大小，RELEASE table 包含超过 200 万条记录
如何提高此查询的性能？
更新
尼克斯的建议奏效了
SELECT DISTINCT t1.entity1 as recordingId,
t1.entity0 as artistId, t2.id as linkid,
t3.name as type,
t4.name,
t4.sort_name,
t4.gid,
t9.latinname as latinName,
t9.islatin,
t7.name as linkattribute,
at.name as artistType
FROM
(
SELECT t1.*
FROM recording_release rr
INNER JOIN l_artist_recording t1 on t1.entity1=rr.recording_id
WHERE rr.release_id between ? AND ?
) AS t1
INNER JOIN link t2 on t1.link=t2.id
INNER JOIN link_type t3 on t2.link_type=t3.id
AND (t3.name='performer' OR t3.name='instrument' OR t3.name='vocal' )
LEFT JOIN link_attribute t6 ON t6.link = t2.id
LEFT JOIN link_attribute_type t7 ON t6.attribute_type = t7.id
INNER JOIN artist t4 on t1.entity0=t4.id
INNER JOIN artist_latin t9 on t9.id=t4.id
LEFT JOIN artist_type at on t4.type=at.id
ORDER BY recordingId, artistId, linkid, linkattribute;
更新 2
好的，它在执行 1 到 100 条记录时工作正常，但这只是测试的临时限制，因为它 运行 太慢了。
当增加到 1 到 1000（这仍然比正常的批量大小 20, 000 小得多）时花费了 13 秒，虽然这比之前好得多仍然比所有其他查询慢得多，即使在 1000 条记录时也只需要不到一秒的时间。
所以这里似乎还有一些潜在的问题导致了问题
解释新的 Sql 1 到 100 个查询
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Unique (cost=49182.37..49183.00 rows=21 width=99) (actual time=917.393..920.229 rows=1271 loops=1)
Buffers: shared hit=21647
-> Sort (cost=49182.37..49182.43 rows=21 width=99) (actual time=917.390..918.206 rows=1286 loops=1)
Sort Key: t1.entity1, t1.entity0, t2.id, t7.name, t3.name, t4.name, t4.sort_name, t4.gid, t9.latinname, t9.islatin, at.name
Sort Method: quicksort Memory: 245kB
Buffers: shared hit=21647
-> Hash Left Join (cost=9574.07..49181.91 rows=21 width=99) (actual time=861.507..915.523 rows=1286 loops=1)
Hash Cond: (t4.type = at.id)
Buffers: shared hit=21629
-> Nested Loop (cost=9572.93..49180.54 rows=21 width=96) (actual time=861.479..913.388 rows=1286 loops=1)
Buffers: shared hit=21628
-> Nested Loop (cost=9572.50..49028.19 rows=21 width=86) (actual time=861.455..904.887 rows=1286 loops=1)
Buffers: shared hit=16484
-> Hash Left Join (cost=9572.08..48875.86 rows=21 width=34) (actual time=861.419..895.695 rows=1286 loops=1)
Hash Cond: (t6.attribute_type = t7.id)
Buffers: shared hit=11340
-> Nested Loop Left Join (cost=9530.00..48833.50 rows=21 width=28) (actual time=859.792..891.958 rows=1286 loops=1)
Buffers: shared hit=11320
-> Hash Join (cost=9529.58..48752.33 rows=21 width=24) (actual time=859.709..884.275 rows=1232 loops=1)
Hash Cond: (t1.link = t2.id)
Buffers: shared hit=7623
-> Nested Loop (cost=0.87..39213.26 rows=2708 width=12) (actual time=0.043..12.256 rows=2559 loops=1)
Buffers: shared hit=4005
-> Index Scan using recording_release_release_id on recording_release rr (cost=0.44..1833.24 rows=891 width=4) (actual time=0.020..1.477 rows=825 loops=1)
Index Cond: ((release_id >= 1) AND (release_id <= 100))
Buffers: shared hit=251
-> Index Scan using l_artist_recording_entity1_idx on l_artist_recording t1 (cost=0.43..41.84 rows=11 width=12) (actual time=0.003..0.007 rows=3 loops=825)
Index Cond: (entity1 = rr.recording_id)
Buffers: shared hit=3754
-> Hash (cost=9487.20..9487.20 rows=3321 width=16) (actual time=859.601..859.601 rows=179079 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 8069kB
Buffers: shared hit=3618
-> Hash Join (cost=23.60..9487.20 rows=3321 width=16) (actual time=0.095..721.936 rows=179079 loops=1)
Hash Cond: (t2.link_type = t3.id)
Buffers: shared hit=3618
-> Seq Scan on link t2 (cost=0.00..7842.74 rows=423374 width=8) (actual time=0.003..286.605 rows=423374 loops=1)
Buffers: shared hit=3609
-> Hash (cost=23.55..23.55 rows=4 width=16) (actual time=0.075..0.075 rows=6 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 1kB
Buffers: shared hit=9
-> Bitmap Heap Scan on link_type t3 (cost=12.84..23.55 rows=4 width=16) (actual time=0.044..0.068 rows=6 loops=1)
Recheck Cond: (((name)::text = 'performer'::text) OR ((name)::text = 'instrument'::text) OR ((name)::text = 'vocal'::text))
Buffers: shared hit=9
-> BitmapOr (cost=12.84..12.84 rows=4 width=0) (actual time=0.032..0.032 rows=0 loops=1)
Buffers: shared hit=6
-> Bitmap Index Scan on link_type_name_idx (cost=0.00..4.28 rows=1 width=0) (actual time=0.015..0.015 rows=2 loops=1)
Index Cond: ((name)::text = 'performer'::text)
Buffers: shared hit=2
-> Bitmap Index Scan on link_type_name_idx (cost=0.00..4.28 rows=1 width=0) (actual time=0.012..0.012 rows=2 loops=1)
Index Cond: ((name)::text = 'instrument'::text)
Buffers: shared hit=2
-> Bitmap Index Scan on link_type_name_idx (cost=0.00..4.28 rows=1 width=0) (actual time=0.003..0.003 rows=2 loops=1)
Index Cond: ((name)::text = 'vocal'::text)
Buffers: shared hit=2
-> Index Only Scan using link_attribute_pkey on link_attribute t6 (cost=0.42..3.84 rows=2 width=8) (actual time=0.003..0.003 rows=1 loops=1232)
Index Cond: (link = t2.id)
Heap Fetches: 0
Buffers: shared hit=3697
-> Hash (cost=29.81..29.81 rows=981 width=14) (actual time=1.602..1.602 rows=981 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 47kB
Buffers: shared hit=20
-> Seq Scan on link_attribute_type t7 (cost=0.00..29.81 rows=981 width=14) (actual time=0.011..0.827 rows=981 loops=1)
Buffers: shared hit=20
-> Index Scan using artist_pkey on artist t4 (cost=0.43..7.24 rows=1 width=52) (actual time=0.003..0.004 rows=1 loops=1286)
Index Cond: (id = t1.entity0)
Buffers: shared hit=5144
-> Index Scan using artist_latin_pkey on artist_latin t9 (cost=0.43..7.24 rows=1 width=18) (actual time=0.003..0.004 rows=1 loops=1286)
Index Cond: (id = t1.entity0)
Buffers: shared hit=5144
-> Hash (cost=1.06..1.06 rows=6 width=11) (actual time=0.014..0.014 rows=6 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 1kB
Buffers: shared hit=1
-> Seq Scan on artist_type at (cost=0.00..1.06 rows=6 width=11) (actual time=0.003..0.007 rows=6 loops=1)
Buffers: shared hit=1
Total runtime: 922.078 ms
(75 rows)
解释新的 Sql 1 到 1000 个查询
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Unique (cost=213157.51..213163.93 rows=214 width=99) (actual time=27763.225..27797.833 rows=11003 loops=1)
Buffers: shared hit=186910 read=59034, temp read=26077 written=26047
-> Sort (cost=213157.51..213158.04 rows=214 width=99) (actual time=27763.223..27774.013 rows=17087 loops=1)
Sort Key: t1.entity1, t1.entity0, t2.id, t7.name, t3.name, t4.name, t4.sort_name, t4.gid, t9.latinname, t9.islatin, at.name
Sort Method: quicksort Memory: 3291kB
Buffers: shared hit=186910 read=59034, temp read=26077 written=26047
-> Hash Left Join (cost=184770.48..213149.22 rows=214 width=99) (actual time=26757.748..27732.727 rows=17087 loops=1)
Hash Cond: (t4.type = at.id)
Buffers: shared hit=186892 read=59034, temp read=26077 written=26047
-> Nested Loop (cost=184769.35..213145.63 rows=214 width=96) (actual time=26757.717..27705.989 rows=17087 loops=1)
Buffers: shared hit=186891 read=59034, temp read=26077 written=26047
-> Nested Loop (cost=184768.92..211593.13 rows=214 width=86) (actual time=26757.687..27597.879 rows=17087 loops=1)
Buffers: shared hit=118447 read=59034, temp read=26077 written=26047
-> Hash Left Join (cost=184768.49..210040.78 rows=214 width=34) (actual time=26757.646..27484.937 rows=17087 loops=1)
Hash Cond: (t6.attribute_type = t7.id)
Buffers: shared hit=50080 read=59034, temp read=26077 written=26047
-> Nested Loop Left Join (cost=184726.42..209995.76 rows=214 width=28) (actual time=26756.055..27456.678 rows=17087 loops=1)
Buffers: shared hit=50060 read=59034, temp read=26077 written=26047
-> Hash Join (cost=184726.00..209168.66 rows=214 width=24) (actual time=26756.000..27370.294 rows=14507 loops=1)
Hash Cond: (rr.recording_id = t1.entity1)
Buffers: shared hit=6525 read=59034, temp read=26077 written=26047
-> Index Scan using recording_release_release_id on recording_release rr (cost=0.44..17820.60 rows=8992 width=4) (actual time=0.019..13.477 rows=10502 loops=1)
Index Cond: ((release_id >= 1) AND (release_id <= 1000))
Buffers: shared hit=2416
-> Hash (cost=184035.19..184035.19 rows=55230 width=24) (actual time=26755.546..26755.546 rows=3637342 loops=1)
Buckets: 8192 Batches: 16 (originally 1) Memory Usage: 20481kB
Buffers: shared hit=4109 read=59034, temp written=17302
-> Hash Join (cost=9528.71..184035.19 rows=55230 width=24) (actual time=850.530..23553.356 rows=3637342 loops=1)
Hash Cond: (t1.link = t2.id)
Buffers: shared hit=4109 read=59034
-> Seq Scan on l_artist_recording t1 (cost=0.00..129942.91 rows=7041791 width=12) (actual time=0.027..4867.525 rows=7041650 loops=1)
Buffers: shared hit=491 read=59034
-> Hash (cost=9487.20..9487.20 rows=3321 width=16) (actual time=850.421..850.421 rows=179079 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 8069kB
Buffers: shared hit=3618
-> Hash Join (cost=23.60..9487.20 rows=3321 width=16) (actual time=0.100..713.303 rows=179079 loops=1)
Hash Cond: (t2.link_type = t3.id)
Buffers: shared hit=3618
-> Seq Scan on link t2 (cost=0.00..7842.74 rows=423374 width=8) (actual time=0.003..281.553 rows=423374 loops=1)
Buffers: shared hit=3609
-> Hash (cost=23.55..23.55 rows=4 width=16) (actual time=0.079..0.079 rows=6 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 1kB
Buffers: shared hit=9
-> Bitmap Heap Scan on link_type t3 (cost=12.84..23.55 rows=4 width=16) (actual time=0.042..0.070 rows=6 loops=1)
Recheck Cond: (((name)::text = 'performer'::text) OR ((name)::text = 'instrument'::text) OR ((name)::text = 'vocal'::text))
Buffers: shared hit=9
-> BitmapOr (cost=12.84..12.84 rows=4 width=0) (actual time=0.034..0.034 rows=0 loops=1)
Buffers: shared hit=6
-> Bitmap Index Scan on link_type_name_idx (cost=0.00..4.28 rows=1 width=0) (actual time=0.016..0.016 rows=2 loops=1)
Index Cond: ((name)::text = 'performer'::text)
Buffers: shared hit=2
-> Bitmap Index Scan on link_type_name_idx (cost=0.00..4.28 rows=1 width=0) (actual time=0.011..0.011 rows=2 loops=1)
Index Cond: ((name)::text = 'instrument'::text)
Buffers: shared hit=2
-> Bitmap Index Scan on link_type_name_idx (cost=0.00..4.28 rows=1 width=0) (actual time=0.003..0.003 rows=2 loops=1)
Index Cond: ((name)::text = 'vocal'::text)
Buffers: shared hit=2
-> Index Only Scan using link_attribute_pkey on link_attribute t6 (cost=0.42..3.84 rows=2 width=8) (actual time=0.002..0.003 rows=1 loops=14507)
Index Cond: (link = t2.id)
Heap Fetches: 0
Buffers: shared hit=43535
-> Hash (cost=29.81..29.81 rows=981 width=14) (actual time=1.568..1.568 rows=981 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 47kB
Buffers: shared hit=20
-> Seq Scan on link_attribute_type t7 (cost=0.00..29.81 rows=981 width=14) (actual time=0.010..0.785 rows=981 loops=1)
Buffers: shared hit=20
-> Index Scan using artist_pkey on artist t4 (cost=0.43..7.24 rows=1 width=52) (actual time=0.003..0.004 rows=1 loops=17087)
Index Cond: (id = t1.entity0)
Buffers: shared hit=68367
-> Index Scan using artist_latin_pkey on artist_latin t9 (cost=0.43..7.24 rows=1 width=18) (actual time=0.003..0.004 rows=1 loops=17087)
Index Cond: (id = t1.entity0)
Buffers: shared hit=68444
-> Hash (cost=1.06..1.06 rows=6 width=11) (actual time=0.013..0.013 rows=6 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 1kB
Buffers: shared hit=1
-> Seq Scan on artist_type at (cost=0.00..1.06 rows=6 width=11) (actual time=0.003..0.006 rows=6 loops=1)
Buffers: shared hit=1
Total runtime: 27805.582 ms
(78 rows)
更新 3
根据帕特里克的建议，此查询对 100 条记录运行良好，对于 1000 条记录，它仍然很慢，但在 12 秒时稍快一些
SELECT DISTINCT t1.entity1 as recordingId,
t1.entity0 as artistId,
t2.id as linkid,
t3.name as type,
t4.name,
t4.sort_name,
t4.gid,
t9.latinname as latinName,
t9.islatin,
t7.name as linkattribute,
at.name as artistType
FROM recording_release rr
INNER JOIN l_artist_recording t1 on t1.entity1=rr.recording_id
AND rr.release_id between ? AND ?
INNER JOIN link t2 on t1.link=t2.id
INNER JOIN link_type t3 on t2.link_type=t3.id
AND (t3.name='performer' OR t3.name='instrument' OR t3.name='vocal' )
LEFT JOIN link_attribute t6
ON t6.link = t2.id
LEFT JOIN link_attribute_type t7
ON t6.attribute_type = t7.id
INNER JOIN artist t4 on t1.entity0=t4.id
INNER JOIN artist_latin t9 on t9.id=t4.id
LEFT JOIN artist_type at on t4.type=at.id
ORDER BY recordingId, artistId, linkid, linkattribute;
在某些情况下，数据库统计信息无法轻松确定使用占位符时为中间查询返回的行数。因此，有时会返回一个非最佳解释计划。
如果您将查询更新为内部联接的子选择，您应该会看到更好的结果。
Inner Join (select <your cols> from recording_release where release_id between ? and ?) rr
在 JOIN 子句中添加条件（过滤器）可以帮助优化器弥补不足，而且我发现它比子查询更短且更易读。
INNER JOIN link_type t3 on t2.link_type=t3.id
AND (t3.name='performer' OR t3.name='instrument' OR t3.name='vocal' )
--Major rework a la @joop
WITH selected AS (
SELECT ar.entity1, ar.entity0, ar.link
FROM l_artist_recording ar
WHERE EXISTS (
SELECT *
FROM recording_release rr
WHERE ar.entity1=rr.recording_id
AND rr.release_id between ? AND ?
)
)
SELECT sel.entity1 as recordingId
, sel.entity0 as artistId
, lnk.id as linkid
, atyp.name as artistType
, rol.name as roletype
, art.name as artname
, art.sort_name
, art.gid
, lat.latinname as latinName
, lat.islatin
, att.name as linkattribute
FROM selected sel
JOIN artist art on art.id = sel.entity0
JOIN artist_latin lat on lat.id= art.id
JOIN link lnk on lnk.id = sel.link
JOIN link_type rol on rol.id = lnk.link_type AND rol.name IN ('performer', 'instrument', 'vocal' )
LEFT JOIN link_attribute la ON la.link = lnk.id
/*LEFT*/ JOIN link_attribute_type att ON att.id = la.attribute_type
LEFT JOIN artist_type atyp on atyp.id = art.type
ORDER BY 1,2,3,4
;
-- The same without the CTE:
SELECT sel.entity1 as recordingId
, sel.entity0 as artistId
, lnk.id as linkid
, atyp.name as artistType
, rol.name as roletype
, art.name as artname
, art.sort_name
, art.gid
, lat.latinname as latinName
, lat.islatin
, att.name as linkattribute
FROM (
SELECT ar.entity1, ar.entity0 , ar.link
FROM l_artist_recording ar
WHERE EXISTS (
SELECT *
FROM recording_release rr
WHERE ar.entity1=rr.recording_id
AND rr.release_id between ? AND ?
)
) sel
JOIN artist art on art.id = sel.entity0
JOIN artist_latin lat on lat.id= art.id
JOIN link lnk on lnk.id = sel.link
JOIN link_type rol on rol.id = lnk.link_type AND rol.name IN ('performer', 'instrument', 'vocal' )
LEFT JOIN link_attribute la ON la.link = lnk.id
/*LEFT*/ JOIN link_attribute_type att ON att.id = la.attribute_type
LEFT JOIN artist_type atyp on atyp.id = art.type
ORDER BY 1,2,3,4
;
- 如果 CTE 中的选定集相对较小，则查询可以从 CTE 中获益。
- 如果您得到重复项，则说明您的查询有问题（其中一个查找表缺少 JOIN 条件）而不是添加
DISTINCT 您应该通过添加此条件来解决它。
我在 Postgres SQL 数据库上执行了一些查询，大多数查询执行得非常快，但有一个执行得非常慢。即使在测试时我只限制主版本 table 的 100 条记录（所有查询都基于版本 table），它也需要 50 秒 ，而所有其他查询都不到一秒
这是键table，其中包含多行
l_artist_recording
Column | Type | Modifiers
----------------+--------------------------+-----------------------------------------------------------------
id | integer | not null default nextval('l_artist_recording_id_seq'::regclass)
link | integer | not null
entity0 | integer | not null
entity1 | integer | not null
edits_pending | integer | not null default 0
last_updated | timestamp with time zone | default now()
link_order | integer | not null default 0
entity0_credit | text | not null default ''::text
entity1_credit | text | not null default ''::text
Indexes:
"l_artist_recording_pkey" PRIMARY KEY, btree (id)
"l_artist_recording_idx_uniq" UNIQUE, btree (entity0, entity1, link, link_order)
"l_artist_recording_entity1_idx" btree (entity1)
"l_artist_recording_idx_entity1" btree (entity1)
"l_artist_recording_link" btree (link)
Check constraints:
"l_artist_recording_edits_pending_check" CHECK (edits_pending >= 0)
"l_artist_recording_link_order_check" CHECK (link_order >= 0)
recording_release
Table "musicbrainz.recording_release"
Column | Type | Modifiers
--------------+---------+-----------
recording_id | integer | not null
release_id | integer | not null
Indexes:
"recording_release_pkey" PRIMARY KEY, btree (recording_id, release_id)
"recording_release_recording_id" btree (recording_id)
"recording_release_release_id" btree (release_id)
艺术家
Column | Type | Modifiers
------------------+--------------------------+-----------------------------------------------------
id | integer | not null default nextval('artist_id_seq'::regclass)
gid | uuid | not null
name | character varying | not null
sort_name | character varying | not null
begin_date_year | smallint |
begin_date_month | smallint |
begin_date_day | smallint |
end_date_year | smallint |
end_date_month | smallint |
end_date_day | smallint |
type | integer |
area | integer |
gender | integer |
comment | character varying(255) | not null default ''::character varying
edits_pending | integer | not null default 0
last_updated | timestamp with time zone | default now()
ended | boolean | not null default false
begin_area | integer |
end_area | integer |
Indexes:
"artist_pkey" PRIMARY KEY, btree (id)
"artist_idx_gid" UNIQUE, btree (gid)
"artist_idx_area" btree (area)
"artist_idx_begin_area" btree (begin_area)
"artist_idx_end_area" btree (end_area)
"artist_idx_lower_name" btree (lower(name::text))
"artist_idx_name" btree (name)
"artist_idx_sort_name" btree (sort_name)
Check constraints:
"artist_edits_pending_check" CHECK (edits_pending >= 0)
"artist_ended_check" CHECK ((end_date_year IS NOT NULL OR end_date_month IS NOT NULL OR end_date_day IS NOT NULL) AND ended = true OR end_date_year IS NULL AND end_date_month IS NULL AND end_date_day IS NULL)
这是我的查询
SELECT DISTINCT t1.entity1 as recordingId,
t1.entity0 as artistId,
t2.id as linkid,
t3.name as type,
t4.name,
t4.sort_name,
t4.gid,
t9.latinname as latinName,
t9.islatin,
t7.name as linkattribute,
at.name as artistType
FROM l_artist_recording t1
INNER JOIN link t2 on t1.link=t2.id
INNER JOIN link_type t3 on t2.link_type=t3.id
AND (t3.name='performer' OR t3.name='instrument' OR t3.name='vocal' )
LEFT JOIN link_attribute t6
ON t6.link = t2.id
LEFT JOIN link_attribute_type t7
ON t6.attribute_type = t7.id
INNER JOIN artist t4 on t1.entity0=t4.id
INNER JOIN artist_latin t9 on t9.id=t4.id
LEFT JOIN artist_type at on t4.type=at.id
INNER JOIN recording t5 on t1.entity1=t5.id
INNER JOIN recording_release rr ON t5.id = rr.recording_id
WHERE rr.release_id BETWEEN ? AND ?
ORDER BY recordingId, artistId, linkid, linkattribute";
我已经检查了所有 table 以确保它们在要连接的任何字段上都有索引，在少数情况下它丢失了所以我添加了。我也在那些 table 上 运行 VACUUM ANALYZE 但这没有什么区别。
这是我的解释（分析、缓冲）输出
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Unique (cost=336796.42..336797.05 rows=21 width=99) (actual time=93229.472..93233.580 rows=1271 loops=1)
Buffers: shared hit=5215 read=97399, temp read=138990 written=138908
-> Sort (cost=336796.42..336796.48 rows=21 width=99) (actual time=93229.468..93230.653 rows=1286 loops=1)
Sort Key: t1.entity1, t1.entity0, t2.id, t7.name, t3.name, t4.name, t4.sort_name, t4.gid, t9.latinname, t9.islatin, at.name
Sort Method: quicksort Memory: 245kB
Buffers: shared hit=5215 read=97399, temp read=138990 written=138908
-> Nested Loop (cost=334176.87..336795.96 rows=21 width=99) (actual time=91632.892..93226.628 rows=1286 loops=1)
Buffers: shared hit=5197 read=97399, temp read=138990 written=138908
-> Hash Join (cost=334176.44..336665.45 rows=21 width=103) (actual time=91632.830..93211.718 rows=1286 loops=1)
Hash Cond: (rr.recording_id = t1.entity1)
Buffers: shared hit=151 read=97315, temp read=138990 written=138908
-> Index Scan using recording_release_release_id on recording_release rr (cost=0.44..1833.24 rows=891 width=4) (actual time=0.028..2.371 rows=825 loops=1)
Index Cond: ((release_id >= 1) AND (release_id <= 100))
Buffers: shared hit=130 read=121
-> Hash (cost=333485.62..333485.62 rows=55230 width=99) (actual time=91631.881..91631.881 rows=3813157 loops=1)
Buckets: 8192 Batches: 32 (originally 1) Memory Usage: 20481kB
Buffers: shared hit=21 read=97194, temp read=61835 written=116275
-> Hash Left Join (cost=132574.41..333485.62 rows=55230 width=99) (actual time=12380.770..84898.987 rows=3813157 loops=1)
Hash Cond: (t4.type = at.id)
.....
这就是问题的症结所在，我的 EXPLAIN 是否告诉我查询会执行得很糟糕，我无法判断，尽管我确实注意到一些我认为是糟糕的顺序扫描。
为了了解数据库的大小，RELEASE table 包含超过 200 万条记录
如何提高此查询的性能？
更新 尼克斯的建议奏效了
SELECT DISTINCT t1.entity1 as recordingId,
t1.entity0 as artistId, t2.id as linkid,
t3.name as type,
t4.name,
t4.sort_name,
t4.gid,
t9.latinname as latinName,
t9.islatin,
t7.name as linkattribute,
at.name as artistType
FROM
(
SELECT t1.*
FROM recording_release rr
INNER JOIN l_artist_recording t1 on t1.entity1=rr.recording_id
WHERE rr.release_id between ? AND ?
) AS t1
INNER JOIN link t2 on t1.link=t2.id
INNER JOIN link_type t3 on t2.link_type=t3.id
AND (t3.name='performer' OR t3.name='instrument' OR t3.name='vocal' )
LEFT JOIN link_attribute t6 ON t6.link = t2.id
LEFT JOIN link_attribute_type t7 ON t6.attribute_type = t7.id
INNER JOIN artist t4 on t1.entity0=t4.id
INNER JOIN artist_latin t9 on t9.id=t4.id
LEFT JOIN artist_type at on t4.type=at.id
ORDER BY recordingId, artistId, linkid, linkattribute;
更新 2 好的，它在执行 1 到 100 条记录时工作正常，但这只是测试的临时限制，因为它 运行 太慢了。
当增加到 1 到 1000（这仍然比正常的批量大小 20, 000 小得多）时花费了 13 秒，虽然这比之前好得多仍然比所有其他查询慢得多，即使在 1000 条记录时也只需要不到一秒的时间。
所以这里似乎还有一些潜在的问题导致了问题
解释新的 Sql 1 到 100 个查询
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Unique (cost=49182.37..49183.00 rows=21 width=99) (actual time=917.393..920.229 rows=1271 loops=1)
Buffers: shared hit=21647
-> Sort (cost=49182.37..49182.43 rows=21 width=99) (actual time=917.390..918.206 rows=1286 loops=1)
Sort Key: t1.entity1, t1.entity0, t2.id, t7.name, t3.name, t4.name, t4.sort_name, t4.gid, t9.latinname, t9.islatin, at.name
Sort Method: quicksort Memory: 245kB
Buffers: shared hit=21647
-> Hash Left Join (cost=9574.07..49181.91 rows=21 width=99) (actual time=861.507..915.523 rows=1286 loops=1)
Hash Cond: (t4.type = at.id)
Buffers: shared hit=21629
-> Nested Loop (cost=9572.93..49180.54 rows=21 width=96) (actual time=861.479..913.388 rows=1286 loops=1)
Buffers: shared hit=21628
-> Nested Loop (cost=9572.50..49028.19 rows=21 width=86) (actual time=861.455..904.887 rows=1286 loops=1)
Buffers: shared hit=16484
-> Hash Left Join (cost=9572.08..48875.86 rows=21 width=34) (actual time=861.419..895.695 rows=1286 loops=1)
Hash Cond: (t6.attribute_type = t7.id)
Buffers: shared hit=11340
-> Nested Loop Left Join (cost=9530.00..48833.50 rows=21 width=28) (actual time=859.792..891.958 rows=1286 loops=1)
Buffers: shared hit=11320
-> Hash Join (cost=9529.58..48752.33 rows=21 width=24) (actual time=859.709..884.275 rows=1232 loops=1)
Hash Cond: (t1.link = t2.id)
Buffers: shared hit=7623
-> Nested Loop (cost=0.87..39213.26 rows=2708 width=12) (actual time=0.043..12.256 rows=2559 loops=1)
Buffers: shared hit=4005
-> Index Scan using recording_release_release_id on recording_release rr (cost=0.44..1833.24 rows=891 width=4) (actual time=0.020..1.477 rows=825 loops=1)
Index Cond: ((release_id >= 1) AND (release_id <= 100))
Buffers: shared hit=251
-> Index Scan using l_artist_recording_entity1_idx on l_artist_recording t1 (cost=0.43..41.84 rows=11 width=12) (actual time=0.003..0.007 rows=3 loops=825)
Index Cond: (entity1 = rr.recording_id)
Buffers: shared hit=3754
-> Hash (cost=9487.20..9487.20 rows=3321 width=16) (actual time=859.601..859.601 rows=179079 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 8069kB
Buffers: shared hit=3618
-> Hash Join (cost=23.60..9487.20 rows=3321 width=16) (actual time=0.095..721.936 rows=179079 loops=1)
Hash Cond: (t2.link_type = t3.id)
Buffers: shared hit=3618
-> Seq Scan on link t2 (cost=0.00..7842.74 rows=423374 width=8) (actual time=0.003..286.605 rows=423374 loops=1)
Buffers: shared hit=3609
-> Hash (cost=23.55..23.55 rows=4 width=16) (actual time=0.075..0.075 rows=6 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 1kB
Buffers: shared hit=9
-> Bitmap Heap Scan on link_type t3 (cost=12.84..23.55 rows=4 width=16) (actual time=0.044..0.068 rows=6 loops=1)
Recheck Cond: (((name)::text = 'performer'::text) OR ((name)::text = 'instrument'::text) OR ((name)::text = 'vocal'::text))
Buffers: shared hit=9
-> BitmapOr (cost=12.84..12.84 rows=4 width=0) (actual time=0.032..0.032 rows=0 loops=1)
Buffers: shared hit=6
-> Bitmap Index Scan on link_type_name_idx (cost=0.00..4.28 rows=1 width=0) (actual time=0.015..0.015 rows=2 loops=1)
Index Cond: ((name)::text = 'performer'::text)
Buffers: shared hit=2
-> Bitmap Index Scan on link_type_name_idx (cost=0.00..4.28 rows=1 width=0) (actual time=0.012..0.012 rows=2 loops=1)
Index Cond: ((name)::text = 'instrument'::text)
Buffers: shared hit=2
-> Bitmap Index Scan on link_type_name_idx (cost=0.00..4.28 rows=1 width=0) (actual time=0.003..0.003 rows=2 loops=1)
Index Cond: ((name)::text = 'vocal'::text)
Buffers: shared hit=2
-> Index Only Scan using link_attribute_pkey on link_attribute t6 (cost=0.42..3.84 rows=2 width=8) (actual time=0.003..0.003 rows=1 loops=1232)
Index Cond: (link = t2.id)
Heap Fetches: 0
Buffers: shared hit=3697
-> Hash (cost=29.81..29.81 rows=981 width=14) (actual time=1.602..1.602 rows=981 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 47kB
Buffers: shared hit=20
-> Seq Scan on link_attribute_type t7 (cost=0.00..29.81 rows=981 width=14) (actual time=0.011..0.827 rows=981 loops=1)
Buffers: shared hit=20
-> Index Scan using artist_pkey on artist t4 (cost=0.43..7.24 rows=1 width=52) (actual time=0.003..0.004 rows=1 loops=1286)
Index Cond: (id = t1.entity0)
Buffers: shared hit=5144
-> Index Scan using artist_latin_pkey on artist_latin t9 (cost=0.43..7.24 rows=1 width=18) (actual time=0.003..0.004 rows=1 loops=1286)
Index Cond: (id = t1.entity0)
Buffers: shared hit=5144
-> Hash (cost=1.06..1.06 rows=6 width=11) (actual time=0.014..0.014 rows=6 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 1kB
Buffers: shared hit=1
-> Seq Scan on artist_type at (cost=0.00..1.06 rows=6 width=11) (actual time=0.003..0.007 rows=6 loops=1)
Buffers: shared hit=1
Total runtime: 922.078 ms
(75 rows)
解释新的 Sql 1 到 1000 个查询
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Unique (cost=213157.51..213163.93 rows=214 width=99) (actual time=27763.225..27797.833 rows=11003 loops=1)
Buffers: shared hit=186910 read=59034, temp read=26077 written=26047
-> Sort (cost=213157.51..213158.04 rows=214 width=99) (actual time=27763.223..27774.013 rows=17087 loops=1)
Sort Key: t1.entity1, t1.entity0, t2.id, t7.name, t3.name, t4.name, t4.sort_name, t4.gid, t9.latinname, t9.islatin, at.name
Sort Method: quicksort Memory: 3291kB
Buffers: shared hit=186910 read=59034, temp read=26077 written=26047
-> Hash Left Join (cost=184770.48..213149.22 rows=214 width=99) (actual time=26757.748..27732.727 rows=17087 loops=1)
Hash Cond: (t4.type = at.id)
Buffers: shared hit=186892 read=59034, temp read=26077 written=26047
-> Nested Loop (cost=184769.35..213145.63 rows=214 width=96) (actual time=26757.717..27705.989 rows=17087 loops=1)
Buffers: shared hit=186891 read=59034, temp read=26077 written=26047
-> Nested Loop (cost=184768.92..211593.13 rows=214 width=86) (actual time=26757.687..27597.879 rows=17087 loops=1)
Buffers: shared hit=118447 read=59034, temp read=26077 written=26047
-> Hash Left Join (cost=184768.49..210040.78 rows=214 width=34) (actual time=26757.646..27484.937 rows=17087 loops=1)
Hash Cond: (t6.attribute_type = t7.id)
Buffers: shared hit=50080 read=59034, temp read=26077 written=26047
-> Nested Loop Left Join (cost=184726.42..209995.76 rows=214 width=28) (actual time=26756.055..27456.678 rows=17087 loops=1)
Buffers: shared hit=50060 read=59034, temp read=26077 written=26047
-> Hash Join (cost=184726.00..209168.66 rows=214 width=24) (actual time=26756.000..27370.294 rows=14507 loops=1)
Hash Cond: (rr.recording_id = t1.entity1)
Buffers: shared hit=6525 read=59034, temp read=26077 written=26047
-> Index Scan using recording_release_release_id on recording_release rr (cost=0.44..17820.60 rows=8992 width=4) (actual time=0.019..13.477 rows=10502 loops=1)
Index Cond: ((release_id >= 1) AND (release_id <= 1000))
Buffers: shared hit=2416
-> Hash (cost=184035.19..184035.19 rows=55230 width=24) (actual time=26755.546..26755.546 rows=3637342 loops=1)
Buckets: 8192 Batches: 16 (originally 1) Memory Usage: 20481kB
Buffers: shared hit=4109 read=59034, temp written=17302
-> Hash Join (cost=9528.71..184035.19 rows=55230 width=24) (actual time=850.530..23553.356 rows=3637342 loops=1)
Hash Cond: (t1.link = t2.id)
Buffers: shared hit=4109 read=59034
-> Seq Scan on l_artist_recording t1 (cost=0.00..129942.91 rows=7041791 width=12) (actual time=0.027..4867.525 rows=7041650 loops=1)
Buffers: shared hit=491 read=59034
-> Hash (cost=9487.20..9487.20 rows=3321 width=16) (actual time=850.421..850.421 rows=179079 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 8069kB
Buffers: shared hit=3618
-> Hash Join (cost=23.60..9487.20 rows=3321 width=16) (actual time=0.100..713.303 rows=179079 loops=1)
Hash Cond: (t2.link_type = t3.id)
Buffers: shared hit=3618
-> Seq Scan on link t2 (cost=0.00..7842.74 rows=423374 width=8) (actual time=0.003..281.553 rows=423374 loops=1)
Buffers: shared hit=3609
-> Hash (cost=23.55..23.55 rows=4 width=16) (actual time=0.079..0.079 rows=6 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 1kB
Buffers: shared hit=9
-> Bitmap Heap Scan on link_type t3 (cost=12.84..23.55 rows=4 width=16) (actual time=0.042..0.070 rows=6 loops=1)
Recheck Cond: (((name)::text = 'performer'::text) OR ((name)::text = 'instrument'::text) OR ((name)::text = 'vocal'::text))
Buffers: shared hit=9
-> BitmapOr (cost=12.84..12.84 rows=4 width=0) (actual time=0.034..0.034 rows=0 loops=1)
Buffers: shared hit=6
-> Bitmap Index Scan on link_type_name_idx (cost=0.00..4.28 rows=1 width=0) (actual time=0.016..0.016 rows=2 loops=1)
Index Cond: ((name)::text = 'performer'::text)
Buffers: shared hit=2
-> Bitmap Index Scan on link_type_name_idx (cost=0.00..4.28 rows=1 width=0) (actual time=0.011..0.011 rows=2 loops=1)
Index Cond: ((name)::text = 'instrument'::text)
Buffers: shared hit=2
-> Bitmap Index Scan on link_type_name_idx (cost=0.00..4.28 rows=1 width=0) (actual time=0.003..0.003 rows=2 loops=1)
Index Cond: ((name)::text = 'vocal'::text)
Buffers: shared hit=2
-> Index Only Scan using link_attribute_pkey on link_attribute t6 (cost=0.42..3.84 rows=2 width=8) (actual time=0.002..0.003 rows=1 loops=14507)
Index Cond: (link = t2.id)
Heap Fetches: 0
Buffers: shared hit=43535
-> Hash (cost=29.81..29.81 rows=981 width=14) (actual time=1.568..1.568 rows=981 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 47kB
Buffers: shared hit=20
-> Seq Scan on link_attribute_type t7 (cost=0.00..29.81 rows=981 width=14) (actual time=0.010..0.785 rows=981 loops=1)
Buffers: shared hit=20
-> Index Scan using artist_pkey on artist t4 (cost=0.43..7.24 rows=1 width=52) (actual time=0.003..0.004 rows=1 loops=17087)
Index Cond: (id = t1.entity0)
Buffers: shared hit=68367
-> Index Scan using artist_latin_pkey on artist_latin t9 (cost=0.43..7.24 rows=1 width=18) (actual time=0.003..0.004 rows=1 loops=17087)
Index Cond: (id = t1.entity0)
Buffers: shared hit=68444
-> Hash (cost=1.06..1.06 rows=6 width=11) (actual time=0.013..0.013 rows=6 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 1kB
Buffers: shared hit=1
-> Seq Scan on artist_type at (cost=0.00..1.06 rows=6 width=11) (actual time=0.003..0.006 rows=6 loops=1)
Buffers: shared hit=1
Total runtime: 27805.582 ms
(78 rows)
更新 3
根据帕特里克的建议，此查询对 100 条记录运行良好，对于 1000 条记录，它仍然很慢，但在 12 秒时稍快一些
SELECT DISTINCT t1.entity1 as recordingId,
t1.entity0 as artistId,
t2.id as linkid,
t3.name as type,
t4.name,
t4.sort_name,
t4.gid,
t9.latinname as latinName,
t9.islatin,
t7.name as linkattribute,
at.name as artistType
FROM recording_release rr
INNER JOIN l_artist_recording t1 on t1.entity1=rr.recording_id
AND rr.release_id between ? AND ?
INNER JOIN link t2 on t1.link=t2.id
INNER JOIN link_type t3 on t2.link_type=t3.id
AND (t3.name='performer' OR t3.name='instrument' OR t3.name='vocal' )
LEFT JOIN link_attribute t6
ON t6.link = t2.id
LEFT JOIN link_attribute_type t7
ON t6.attribute_type = t7.id
INNER JOIN artist t4 on t1.entity0=t4.id
INNER JOIN artist_latin t9 on t9.id=t4.id
LEFT JOIN artist_type at on t4.type=at.id
ORDER BY recordingId, artistId, linkid, linkattribute;
在某些情况下，数据库统计信息无法轻松确定使用占位符时为中间查询返回的行数。因此，有时会返回一个非最佳解释计划。
如果您将查询更新为内部联接的子选择，您应该会看到更好的结果。
Inner Join (select <your cols> from recording_release where release_id between ? and ?) rr
在 JOIN 子句中添加条件（过滤器）可以帮助优化器弥补不足，而且我发现它比子查询更短且更易读。
INNER JOIN link_type t3 on t2.link_type=t3.id
AND (t3.name='performer' OR t3.name='instrument' OR t3.name='vocal' )
--Major rework a la @joop
WITH selected AS (
SELECT ar.entity1, ar.entity0, ar.link
FROM l_artist_recording ar
WHERE EXISTS (
SELECT *
FROM recording_release rr
WHERE ar.entity1=rr.recording_id
AND rr.release_id between ? AND ?
)
)
SELECT sel.entity1 as recordingId
, sel.entity0 as artistId
, lnk.id as linkid
, atyp.name as artistType
, rol.name as roletype
, art.name as artname
, art.sort_name
, art.gid
, lat.latinname as latinName
, lat.islatin
, att.name as linkattribute
FROM selected sel
JOIN artist art on art.id = sel.entity0
JOIN artist_latin lat on lat.id= art.id
JOIN link lnk on lnk.id = sel.link
JOIN link_type rol on rol.id = lnk.link_type AND rol.name IN ('performer', 'instrument', 'vocal' )
LEFT JOIN link_attribute la ON la.link = lnk.id
/*LEFT*/ JOIN link_attribute_type att ON att.id = la.attribute_type
LEFT JOIN artist_type atyp on atyp.id = art.type
ORDER BY 1,2,3,4
;
-- The same without the CTE:
SELECT sel.entity1 as recordingId
, sel.entity0 as artistId
, lnk.id as linkid
, atyp.name as artistType
, rol.name as roletype
, art.name as artname
, art.sort_name
, art.gid
, lat.latinname as latinName
, lat.islatin
, att.name as linkattribute
FROM (
SELECT ar.entity1, ar.entity0 , ar.link
FROM l_artist_recording ar
WHERE EXISTS (
SELECT *
FROM recording_release rr
WHERE ar.entity1=rr.recording_id
AND rr.release_id between ? AND ?
)
) sel
JOIN artist art on art.id = sel.entity0
JOIN artist_latin lat on lat.id= art.id
JOIN link lnk on lnk.id = sel.link
JOIN link_type rol on rol.id = lnk.link_type AND rol.name IN ('performer', 'instrument', 'vocal' )
LEFT JOIN link_attribute la ON la.link = lnk.id
/*LEFT*/ JOIN link_attribute_type att ON att.id = la.attribute_type
LEFT JOIN artist_type atyp on atyp.id = art.type
ORDER BY 1,2,3,4
;
- 如果 CTE 中的选定集相对较小，则查询可以从 CTE 中获益。
- 如果您得到重复项，则说明您的查询有问题（其中一个查找表缺少 JOIN 条件）而不是添加
DISTINCT您应该通过添加此条件来解决它。