我正在尝试创建一个新表，它是具有匹配主键的其他6个表的总和。如果我使用3个以上的输入表，这就会停滞不前：
CREATE TABLE table_name AS SELECT table1.timestamp, table1.value + table2.value + table3.value + table4.value AS value FROM table1, table2, table3, table4 WHERE table1.timestamp=table2.timestamp AND table2.timestamp=table3.timestamp AND table3.timestamp=table4.timestamp;
问题：当运行2-3个表时，脚本运行得相当快（<5秒），否则会停止。我没有尝试过超过5分钟的运行时间，但这对我的目的来说太慢了。
表格说明：每个表格的格式相同，共有6列（其中2列相关）。主键是整数“时间戳”，“值”是实数。表大小各不相同，但每个表的悬停量大约为100万行/条目。这些表大多具有相同的主键，但每个表中缺少一些数据点，因此从新表中省略这些数据点至关重要。
我做错了什么，我该怎么办才能让它快速运行？
修改
Ps：这是完整的“EXPLAIN ANALYZE”查询的实际输出：
eldb=# EXPLAIN ANALYZE CREATE TABLE test_table AS SELECT count1.timestamp, count
1.year, count1.month, count1.day, count1.period, count1.the_value + count2.the_value + count
3.the_value + count4.the_value + count5.the_value + count6.the_value AS the_value FROM "table_name-1" AS count
1, "table_name-2" AS count2, "table_name-3" AS count3, "table_name-4" AS count4,
"table_name-5" AS count5, "table_name-6" AS count6 WHERE count1.timestamp=count
2.timestamp AND count2.timestamp=count3.timestamp AND count3.timestamp=count4.ti
mestamp AND count4.timestamp=count5.timestamp AND count5.timestamp=count6.timest
amp AND count1.timestamp>2012020000 AND count2.timestamp>2012020000 AND count3.t
imestamp>2012020000 AND count4.timestamp>2012020000 and count5.timestamp>2012020
000 AND count6.timestamp>2012020000;
QUERY
PLAN
--------------------------------------------------------------------------------
------------------------------------------------------------------------------
Merge Join (cost=20323.61..153806457715456.50 rows=5592655588099248 width=44)
(actual time=84.524..3310.692 rows=3410 loops=1)
Merge Cond: (count1."timestamp" = count4."timestamp")
-> Nested Loop (cost=10161.80..4417379579.26 rows=1057606343 width=40) (act
ual time=44.597..1616.585 rows=3410 loops=1)
Join Filter: (count2."timestamp" = count1."timestamp")
-> Merge Join (cost=10161.80..101480.96 rows=6070522 width=16) (actua
l time=43.648..48.950 rows=3410 loops=1)
Merge Cond: (count2."timestamp" = count3."timestamp")
-> Sort (cost=5080.90..5168.01 rows=34844 width=8) (actual time
=25.608..25.804 rows=3410 loops=1)
Sort Key: count2."timestamp"
Sort Method: quicksort Memory: 256kB
-> Seq Scan on "table_name-2" count2 (cost=0.00..1972.66
rows=34844 width=8) (actual time=0.064..23.297 rows=3410 loops=1)
Filter: ("timestamp" > 2012020000)
-> Materialize (cost=5080.90..5255.12 rows=34844 width=8) (actu
al time=18.030..19.847 rows=3410 loops=1)
-> Sort (cost=5080.90..5168.01 rows=34844 width=8) (actua
l time=18.023..18.416 rows=3410 loops=1)
Sort Key: count3."timestamp"
Sort Method: quicksort Memory: 256kB
-> Seq Scan on "table_name-3" count3 (cost=0.00..19
72.66 rows=34844 width=8) (actual time=0.023..16.294 rows=3410 loops=1)
Filter: ("timestamp" > 2012020000)
-> Materialize (cost=0.00..2351.88 rows=34844 width=24) (actual time=
0.000..0.147 rows=3410 loops=3410)
-> Seq Scan on "table_name-1" count1 (cost=0.00..1972.66 rows=3
4844 width=24) (actual time=0.020..16.853 rows=3410 loops=1)
Filter: ("timestamp" > 2012020000)
-> Materialize (cost=10161.80..4007228099.11 rows=1057606343 width=24) (act
ual time=39.917..1687.402 rows=3410 loops=1)
-> Nested Loop (cost=10161.80..4004584083.26 rows=1057606343 width=24
) (actual time=39.915..1685.956 rows=3410 loops=1)
Join Filter: (count4."timestamp" = count6."timestamp")
-> Merge Join (cost=10161.80..101480.96 rows=6070522 width=16)
(actual time=38.689..44.309 rows=3410 loops=1)
Merge Cond: (count4."timestamp" = count5."timestamp")
-> Sort (cost=5080.90..5168.01 rows=34844 width=8) (actua
l time=18.960..19.156 rows=3410 loops=1)
Sort Key: count4."timestamp"
Sort Method: quicksort Memory: 256kB
-> Seq Scan on "table_name-4" count4 (cost=0.00..19
72.66 rows=34844 width=8) (actual time=0.059..17.271 rows=3410 loops=1)
Filter: ("timestamp" > 2012020000)
-> Materialize (cost=5080.90..5255.12 rows=34844 width=8)
(actual time=19.717..21.826 rows=3410 loops=1)
-> Sort (cost=5080.90..5168.01 rows=34844 width=8)
(actual time=19.708..20.266 rows=3410 loops=1)
Sort Key: count5."timestamp"
Sort Method: quicksort Memory: 256kB
-> Seq Scan on "table_name-5" count5 (cost=0.
00..1972.66 rows=34844 width=8) (actual time=0.034..18.001 rows=3410 loops=1)
Filter: ("timestamp" > 2012020000)
-> Materialize (cost=0.00..2283.88 rows=34844 width=8) (actual
time=0.000..0.148 rows=3410 loops=3410)
-> Seq Scan on "table_name-6" count6 (cost=0.00..1972.66
rows=34844 width=8) (actual time=0.036..17.785 rows=3410 loops=1)
Filter: ("timestamp" > 2012020000)
Total runtime: 3330.933 ms
(40 rows)
这是表结构（对所有表都相同）：
CREATE TABLE "table_name-6"
(
"timestamp" integer NOT NULL,
year integer NOT NULL,
month integer NOT NULL,
day integer NOT NULL,
period integer NOT NULL,
the_value real,
CONSTRAINT "table_name-6_pkey" PRIMARY KEY ("timestamp" )
)
注意：实际的表名和值已重命名。此外，此输出仅占实际表格大小的一小部分。
答案 0 :(得分：3)
DROP SCHEMA tmp CASCADE;
CREATE SCHEMA tmp ;
set search_path='tmp';
SET random_page_cost=1;
CREATE TABLE table_name1
( ztimestamp integer NOT NULL
, year integer NOT NULL
, month integer NOT NULL
, day integer NOT NULL
, period integer NOT NULL
, the_value real
, CONSTRAINT table_name1_pkey PRIMARY KEY (ztimestamp )
) ;
CREATE TABLE table_name2
( ztimestamp integer NOT NULL
, year integer NOT NULL
, month integer NOT NULL
, day integer NOT NULL
, period integer NOT NULL
, the_value real
, CONSTRAINT table_name2_pkey PRIMARY KEY (ztimestamp )
) ;
... similar for 3,4,5,6 ...
INSERT INTO table_name1(ztimestamp,year,month,day,period,the_value)
SELECT generate_series(1,2000), 0,0,0,0, 1.0;
INSERT INTO table_name2 SELECT * FROM table_name1;
INSERT INTO table_name3 SELECT * FROM table_name1;
INSERT INTO table_name4 SELECT * FROM table_name1;
INSERT INTO table_name5 SELECT * FROM table_name1;
INSERT INTO table_name6 SELECT * FROM table_name1;
EXPLAIN ANALYZE
CREATE TABLE test_table AS
SELECT c1.ztimestamp, c1.year, c1.month, c1.day, c1.period
, c1.the_value + c2.the_value + c3.the_value + c4.the_value
+ c5.the_value + c6.the_value AS the_value
FROM table_name1 AS c1
, table_name2 AS c2
, table_name3 AS c3
, table_name4 AS c4
, table_name5 AS c5
, table_name6 AS c6
WHERE c1.ztimestamp=c2.ztimestamp
AND c2.ztimestamp=c3.ztimestamp
AND c3.ztimestamp=c4.ztimestamp
AND c4.ztimestamp=c5.ztimestamp
AND c5.ztimestamp=c6.ztimestamp
;
结果＆amp;＆amp;计划：INSERT 0 2000
INSERT 0 2000
INSERT 0 2000
INSERT 0 2000
INSERT 0 2000
INSERT 0 2000
INSERT 0 2000
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------
Merge Join (cost=0.00..475.93 rows=1963 width=44) (actual time=0.066..11.840 rows=2000 loops=1)
Merge Cond: (c1.ztimestamp = c6.ztimestamp)
-> Merge Join (cost=0.00..371.26 rows=1963 width=56) (actual time=0.052..8.706 rows=2000 loops=1)
Merge Cond: (c1.ztimestamp = c5.ztimestamp)
-> Merge Join (cost=0.00..291.12 rows=1963 width=48) (actual time=0.042..6.752 rows=2000 loops=1)
Merge Cond: (c1.ztimestamp = c4.ztimestamp)
-> Merge Join (cost=0.00..210.98 rows=1963 width=40) (actual time=0.033..4.751 rows=2000 loops=1)
Merge Cond: (c1.ztimestamp = c3.ztimestamp)
-> Merge Join (cost=0.00..130.84 rows=1963 width=32) (actual time=0.022..2.903 rows=2000 loops=1)
Merge Cond: (c1.ztimestamp = c2.ztimestamp)
-> Index Scan using table_name1_pkey on table_name1 c1 (cost=0.00..50.70 rows=1963 width=24) (actual time=0.009..0.609 rows=2000 loops=1)
-> Index Scan using table_name2_pkey on table_name2 c2 (cost=0.00..50.70 rows=1963 width=8) (actual time=0.010..0.756 rows=2000 loops=1)
-> Index Scan using table_name3_pkey on table_name3 c3 (cost=0.00..50.70 rows=1963 width=8) (actual time=0.010..0.718 rows=2000 loops=1)
-> Index Scan using table_name4_pkey on table_name4 c4 (cost=0.00..50.70 rows=1963 width=8) (actual time=0.009..0.758 rows=2000 loops=1)
-> Index Scan using table_name5_pkey on table_name5 c5 (cost=0.00..50.70 rows=1963 width=8) (actual time=0.010..0.696 rows=2000 loops=1)
-> Index Scan using table_name6_pkey on table_name6 c6 (cost=0.00..50.70 rows=1963 width=8) (actual time=0.008..1.044 rows=2000 loops=1)
Total runtime: 70.201 ms
(17 rows)
更新：大多数人更喜欢JOIN语法到where ...语法：
EXPLAIN ANALYZE
CREATE TABLE test_table AS
SELECT c1.ztimestamp, c1.year, c1.month, c1.day, c1.period
, c1.the_value + c2.the_value + c3.the_value + c4.the_value
+ c5.the_value + c6.the_value AS the_value
FROM table_name1 AS c1
JOIN table_name2 AS c2 ON c1.ztimestamp=c2.ztimestamp
JOIN table_name3 AS c3 ON c2.ztimestamp=c3.ztimestamp
JOIN table_name4 AS c4 ON c3.ztimestamp=c4.ztimestamp
JOIN table_name5 AS c5 ON c4.ztimestamp=c5.ztimestamp
JOIN table_name6 AS c6 ON c5.ztimestamp=c6.ztimestamp
;