是否有人使用tablefunc来转移多个变量而不是仅使用行名？ The documentation notes：
对于具有的所有行，“额外”列应该是相同的 相同的row_name值。
我不知道如何在没有组合我想要转向的列的情况下做到这一点（我非常怀疑它会给我我需要的速度）。一种可行的方法是将实体设为数字，并将其作为毫秒添加到localt，但这似乎是一种不稳定的方式。
我已编辑了对此问题的回复中使用的数据：PostgreSQL Crosstab Query。
CREATE TEMP TABLE t4 (
timeof timestamp
,entity character
,status integer
,ct integer);
INSERT INTO t4 VALUES
('2012-01-01', 'a', 1, 1)
,('2012-01-01', 'a', 0, 2)
,('2012-01-02', 'b', 1, 3)
,('2012-01-02', 'c', 0, 4);
SELECT * FROM crosstab(
'SELECT timeof, entity, status, ct
FROM t4
ORDER BY 1,2,3'
,$$VALUES (1::text), (0::text)$$)
AS ct ("Section" timestamp, "Attribute" character, "1" int, "0" int);
返回：
Section | Attribute | 1 | 0 ---------------------------+-----------+---+--- 2012-01-01 00:00:00 | a | 1 | 2 2012-01-02 00:00:00 | b | 3 | 4
因此，正如文档所述，额外列（又称“属性”）对于每个行名称又称“部分”被假定为相同。因此，它会报告第二行的 b ，即使“实体”还具有该'timeof'值的'c'值。
期望的输出：
Section | Attribute | 1 | 0
--------------------------+-----------+---+---
2012-01-01 00:00:00 | a | 1 | 2
2012-01-02 00:00:00 | b | 3 |
2012-01-02 00:00:00 | c | | 4
有任何想法或参考？
更多背景知识：我可能需要为数十亿行执行此操作，并且我正在测试以长格式和宽格式存储此数据并查看是否可以使用tablefunc比常规聚合函数更有效地从长格式转换为宽格式
对于大约300个实体，我每分钟大约进行100次测量。通常，我们需要比较给定实体的给定秒的不同测量值，因此我们需要经常使用宽格式。此外，对特定实体进行的测量也是高度可变的。
编辑：我找到了一个资源：http://www.postgresonline.com/journal/categories/24-tablefunc。
答案 0 :(得分：11)
您的查询存在的问题是 b 和 c 共享相同的时间戳2012-01-02 00:00:00，而您拥有{ {1}}列timestamp首先在您的查询中，所以 - 即使您添加了大胆的重点 - timeof和b只是属于同一组的额外列c 。自(quoting the manual)以来只返回第一个（2012-01-02 00:00:00）：
b列必须是第一个。row_name和category列必须是最后两列，按此顺序排列。value和row_name之间的任何列都被视为“额外”。对于具有相同category值的所有行，“额外”列预计相同。
大胆强调我的
只需恢复前两列的顺序，即可使row_name成为行名称，并根据需要运行：
entity SELECT * FROM crosstab(
'SELECT entity, timeof, status, ct
FROM t4
ORDER BY 1'
,'VALUES (1), (0)')
AS ct (
"Attribute" character
,"Section" timestamp
,"status_1" int
,"status_0" int);
当然必须是唯一的。
entity 首先 row_name列 next extra（由第二个参数定义）和category 最后。从每个value分区的第一行行填充额外的列。忽略其他行中的值，每个row_name只能填充一列。通常，对于一个row_name的每一行，这些都是相同的，但这取决于你。
row_name难怪你的测试中的查询表现非常糟糕。您的测试设置有14M行，您可以处理所有行，然后使用SELECT localt, entity
, msrmnt01, msrmnt02, msrmnt03, msrmnt04, msrmnt05 -- , more?
FROM crosstab(
'SELECT dense_rank() OVER (ORDER BY localt, entity)::int AS row_name
, localt, entity -- additional columns
, msrmnt, val
FROM test
-- WHERE ??? -- instead of LIMIT at the end
ORDER BY localt, entity, msrmnt
-- LIMIT ???' -- instead of LIMIT at the end
, $$SELECT generate_series(1,5)$$) -- more?
AS ct (row_name int, localt timestamp, entity int
, msrmnt01 float8, msrmnt02 float8, msrmnt03 float8, msrmnt04 float8, msrmnt05 float8 -- , more?
)
LIMIT 1000 -- ??!!
将其中的大部分内容丢弃。对于简化的结果集，在源查询中添加WHERE条件或LIMIT！
另外，你使用的阵列在它之上是不必要的昂贵。我使用dense_rank（）代替生成代理行名称。
db<>fiddle此处 - 使用更简单的测试设置和更少的行。
答案 1 :(得分：11)
在我原来的问题中，我应该将它用于我的样本数据：
CREATE TEMP TABLE t4 (
timeof date
,entity integer
,status integer
,ct integer);
INSERT INTO t4 VALUES
('2012-01-01', 1, 1, 1)
,('2012-01-01', 1, 0, 2)
,('2012-01-01', 3, 0, 3)
,('2012-01-02', 2, 1, 4)
,('2012-01-02', 3, 1, 5)
,('2012-01-02', 3, 0, 6);
有了这个，我必须转向时间和实体。由于tablefunc仅使用一列进行旋转，因此您需要找到一种方法来填充该列中的两个维度。 （http://www.postgresonline.com/journal/categories/24-tablefunc）。我使用了数组，就像该链接中的示例一样。
SELECT (timestamp 'epoch' + row_name[1] * INTERVAL '1 second')::date
as localt,
row_name[2] As entity, status1, status0
FROM crosstab('SELECT ARRAY[extract(epoch from timeof), entity] as row_name,
status, ct
FROM t4
ORDER BY timeof, entity, status'
,$$VALUES (1::text), (0::text)$$)
as ct (row_name integer[], status1 int, status0 int)
FWIW，我尝试使用字符数组，到目前为止，我的设置看起来更快; 9.2.3 Postgresql。
这是结果和期望的输出。
localt | entity | status1 | status0
--------------------------+---------+--------
2012-01-01 | 1 | 1 | 2
2012-01-01 | 3 | | 3
2012-01-02 | 2 | 4 |
2012-01-02 | 3 | 5 | 6
我很好奇这是如何在更大的数据集上执行的，并会在以后报告。
答案 2 :(得分：1)
好的，所以我把它放在靠近我的用例的桌子上。我做错了或者交叉表不适合我使用。
首先我做了一些类似的数据：
CREATE TABLE public.test (
id serial primary key,
msrmnt integer,
entity integer,
localt timestamp,
val double precision
);
CREATE INDEX ix_test_msrmnt
ON public.test (msrmnt);
CREATE INDEX ix_public_test_201201_entity
ON public.test (entity);
CREATE INDEX ix_public_test_201201_localt
ON public.test (localt);
insert into public.test (msrmnt, entity, localt, val)
select *
from(
SELECT msrmnt, entity, localt, random() as val
FROM generate_series('2012-01-01'::timestamp, '2012-01-01 23:59:00'::timestamp, interval '1 minutes') as localt
join
(select *
FROM generate_series(1, 50, 1) as msrmnt) as msrmnt
on 1=1
join
(select *
FROM generate_series(1, 200, 1) as entity) as entity
on 1=1) as data;
然后我运行了几次交叉表代码：
explain analyze
SELECT (timestamp 'epoch' + row_name[1] * INTERVAL '1 second')::date As localt, row_name[2] as entity
,msrmnt01,msrmnt02,msrmnt03,msrmnt04,msrmnt05,msrmnt06,msrmnt07,msrmnt08,msrmnt09,msrmnt10
,msrmnt11,msrmnt12,msrmnt13,msrmnt14,msrmnt15,msrmnt16,msrmnt17,msrmnt18,msrmnt19,msrmnt20
,msrmnt21,msrmnt22,msrmnt23,msrmnt24,msrmnt25,msrmnt26,msrmnt27,msrmnt28,msrmnt29,msrmnt30
,msrmnt31,msrmnt32,msrmnt33,msrmnt34,msrmnt35,msrmnt36,msrmnt37,msrmnt38,msrmnt39,msrmnt40
,msrmnt41,msrmnt42,msrmnt43,msrmnt44,msrmnt45,msrmnt46,msrmnt47,msrmnt48,msrmnt49,msrmnt50
FROM crosstab('SELECT ARRAY[extract(epoch from localt), entity] as row_name, msrmnt, val
FROM public.test
ORDER BY localt, entity, msrmnt',$$VALUES ( 1::text),( 2::text),( 3::text),( 4::text),( 5::text),( 6::text),( 7::text),( 8::text),( 9::text),(10::text)
,(11::text),(12::text),(13::text),(14::text),(15::text),(16::text),(17::text),(18::text),(19::text),(20::text)
,(21::text),(22::text),(23::text),(24::text),(25::text),(26::text),(27::text),(28::text),(29::text),(30::text)
,(31::text),(32::text),(33::text),(34::text),(35::text),(36::text),(37::text),(38::text),(39::text),(40::text)
,(41::text),(42::text),(43::text),(44::text),(45::text),(46::text),(47::text),(48::text),(49::text),(50::text)$$)
as ct (row_name integer[],msrmnt01 double precision, msrmnt02 double precision,msrmnt03 double precision, msrmnt04 double precision,msrmnt05 double precision,
msrmnt06 double precision,msrmnt07 double precision, msrmnt08 double precision,msrmnt09 double precision, msrmnt10 double precision
,msrmnt11 double precision, msrmnt12 double precision,msrmnt13 double precision, msrmnt14 double precision,msrmnt15 double precision,
msrmnt16 double precision,msrmnt17 double precision, msrmnt18 double precision,msrmnt19 double precision, msrmnt20 double precision
,msrmnt21 double precision, msrmnt22 double precision,msrmnt23 double precision, msrmnt24 double precision,msrmnt25 double precision,
msrmnt26 double precision,msrmnt27 double precision, msrmnt28 double precision,msrmnt29 double precision, msrmnt30 double precision
,msrmnt31 double precision, msrmnt32 double precision,msrmnt33 double precision, msrmnt34 double precision,msrmnt35 double precision,
msrmnt36 double precision,msrmnt37 double precision, msrmnt38 double precision,msrmnt39 double precision, msrmnt40 double precision
,msrmnt41 double precision, msrmnt42 double precision,msrmnt43 double precision, msrmnt44 double precision,msrmnt45 double precision,
msrmnt46 double precision,msrmnt47 double precision, msrmnt48 double precision,msrmnt49 double precision, msrmnt50 double precision)
limit 1000
在第三次尝试中获得此信息：
QUERY PLAN
Limit (cost=0.00..20.00 rows=1000 width=432) (actual time=110236.673..110237.667 rows=1000 loops=1)
-> Function Scan on crosstab ct (cost=0.00..20.00 rows=1000 width=432) (actual time=110236.672..110237.598 rows=1000 loops=1)
Total runtime: 110699.598 ms
然后我运行了几次标准溶液：
explain analyze
select localt, entity,
max(case when msrmnt = 1 then val else null end) as msrmnt01
,max(case when msrmnt = 2 then val else null end) as msrmnt02
,max(case when msrmnt = 3 then val else null end) as msrmnt03
,max(case when msrmnt = 4 then val else null end) as msrmnt04
,max(case when msrmnt = 5 then val else null end) as msrmnt05
,max(case when msrmnt = 6 then val else null end) as msrmnt06
,max(case when msrmnt = 7 then val else null end) as msrmnt07
,max(case when msrmnt = 8 then val else null end) as msrmnt08
,max(case when msrmnt = 9 then val else null end) as msrmnt09
,max(case when msrmnt = 10 then val else null end) as msrmnt10
,max(case when msrmnt = 11 then val else null end) as msrmnt11
,max(case when msrmnt = 12 then val else null end) as msrmnt12
,max(case when msrmnt = 13 then val else null end) as msrmnt13
,max(case when msrmnt = 14 then val else null end) as msrmnt14
,max(case when msrmnt = 15 then val else null end) as msrmnt15
,max(case when msrmnt = 16 then val else null end) as msrmnt16
,max(case when msrmnt = 17 then val else null end) as msrmnt17
,max(case when msrmnt = 18 then val else null end) as msrmnt18
,max(case when msrmnt = 19 then val else null end) as msrmnt19
,max(case when msrmnt = 20 then val else null end) as msrmnt20
,max(case when msrmnt = 21 then val else null end) as msrmnt21
,max(case when msrmnt = 22 then val else null end) as msrmnt22
,max(case when msrmnt = 23 then val else null end) as msrmnt23
,max(case when msrmnt = 24 then val else null end) as msrmnt24
,max(case when msrmnt = 25 then val else null end) as msrmnt25
,max(case when msrmnt = 26 then val else null end) as msrmnt26
,max(case when msrmnt = 27 then val else null end) as msrmnt27
,max(case when msrmnt = 28 then val else null end) as msrmnt28
,max(case when msrmnt = 29 then val else null end) as msrmnt29
,max(case when msrmnt = 30 then val else null end) as msrmnt30
,max(case when msrmnt = 31 then val else null end) as msrmnt31
,max(case when msrmnt = 32 then val else null end) as msrmnt32
,max(case when msrmnt = 33 then val else null end) as msrmnt33
,max(case when msrmnt = 34 then val else null end) as msrmnt34
,max(case when msrmnt = 35 then val else null end) as msrmnt35
,max(case when msrmnt = 36 then val else null end) as msrmnt36
,max(case when msrmnt = 37 then val else null end) as msrmnt37
,max(case when msrmnt = 38 then val else null end) as msrmnt38
,max(case when msrmnt = 39 then val else null end) as msrmnt39
,max(case when msrmnt = 40 then val else null end) as msrmnt40
,max(case when msrmnt = 41 then val else null end) as msrmnt41
,max(case when msrmnt = 42 then val else null end) as msrmnt42
,max(case when msrmnt = 43 then val else null end) as msrmnt43
,max(case when msrmnt = 44 then val else null end) as msrmnt44
,max(case when msrmnt = 45 then val else null end) as msrmnt45
,max(case when msrmnt = 46 then val else null end) as msrmnt46
,max(case when msrmnt = 47 then val else null end) as msrmnt47
,max(case when msrmnt = 48 then val else null end) as msrmnt48
,max(case when msrmnt = 49 then val else null end) as msrmnt49
,max(case when msrmnt = 50 then val else null end) as msrmnt50
from sample
group by localt, entity
limit 1000
在第三次尝试中获得此信息：
QUERY PLAN
Limit (cost=2257339.69..2270224.77 rows=1000 width=24) (actual time=19795.984..20090.626 rows=1000 loops=1)
-> GroupAggregate (cost=2257339.69..5968242.35 rows=288000 width=24) (actual time=19795.983..20090.496 rows=1000 loops=1)
-> Sort (cost=2257339.69..2293339.91 rows=14400088 width=24) (actual time=19795.626..19808.820 rows=50001 loops=1)
Sort Key: localt
Sort Method: external merge Disk: 478568kB
-> Seq Scan on sample (cost=0.00..249883.88 rows=14400088 width=24) (actual time=0.013..2245.247 rows=14400000 loops=1)
Total runtime: 20197.565 ms
因此，就我而言，到目前为止看来交叉表不是解决方案。而这只是我有多年的一天。事实上，我可能不得不使用宽格式（非规范化）表格，尽管实体的哪些测量值是可变的并且引入了新的表格，但我不会在这里进行讨论。
以下是使用Postgres 9.2.3的一些设置：
name setting
max_connections 100
shared_buffers 2097152
effective_cache_size 6291456
maintenance_work_mem 1048576
work_mem 262144