Performance Postgresql使用多个WHERE等式创建表AS_Performance_Postgresql_Aggregate Functions_Where_Create Table

Performance Postgresql使用多个WHERE等式创建表AS

performance postgresql

Performance Postgresql使用多个WHERE等式创建表AS,performance,postgresql,aggregate-functions,where,create-table,Performance,Postgresql,Aggregate Functions,Where,Create Table,我正在尝试创建一个新表，它是其他6个具有匹配主键的表的总和。如果我使用了3个以上的输入表，则会一直暂停： 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 A

我正在尝试创建一个新表，它是其他6个具有匹配主键的表的总和。如果我使用了3个以上的输入表，则会一直暂停：

 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：脚本运行速度相当快( 结果和计划：插入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：与where…语法相比，大多数人更喜欢JOIN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
        ;

结果和计划：插入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：与where…语法相比，大多数人更喜欢JOIN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
        ;

如果一个特定的键只出现在四个表中的一个表中，您希望发生什么？我根本不希望该键包含在新表中（即完全跳过它）。（ps：感谢您的快速响应！）时间戳是每个表的主键？您有索引吗？顺便说一句，“timestamp”是一个保留字（类型）在第页。最好避免它们作为标识符。顺便说一句：请添加一个查询计划。您可以通过放置“解释分析”来获得一个在您的查询前面。如果您已将它们定义为主键，PG将自动为它们创建唯一的索引。如果您认为它们只是PK，PG无法知道。我不相信所有的表都有主键，因为查询计划中有排序步骤。如果某个特定的键仅存在于四个表中的一个？我根本不希望该键包含在新表中（即完全跳过它）。（ps：感谢您的快速响应！）时间戳是每个表的主键？它们上有索引吗？顺便说一句，“时间戳”是一个保留字（类型）在第页。最好避免它们作为标识符。顺便说一句：请添加一个查询计划。您可以通过放置“解释分析”来获得一个在您的查询前面。如果您将它们定义为主键，PG将自动为它们创建唯一的索引。如果您认为它们只是PK，PG无法知道。考虑到查询计划中的排序步骤，我不相信所有表都有主键。

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
        ;