我是PostgreSQL的新手，使用的是版本9.4。我有一个收集测量值的表格为字符串，需要使用一些始终是最新的东西将其转换为一种PIVOT表格，如VIEW。
此外，需要转换一些值，例如： G。乘以1000，就像你一样
可以在下面的示例中看到＆＃34; sensor3＆＃34;。
来源表：
CREATE TABLE source (
id bigint NOT NULL,
name character varying(255),
"timestamp" timestamp without time zone,
value character varying(32672),
CONSTRAINT source_pkey PRIMARY KEY (id)
);
INSERT INTO source VALUES
(15,'sensor2','2015-01-03 22:02:05.872','88.4')
, (16,'foo27' ,'2015-01-03 22:02:10.887','-3.755')
, (17,'sensor1','2015-01-03 22:02:10.887','1.1704')
, (18,'foo27' ,'2015-01-03 22:02:50.825','-1.4')
, (19,'bar_18' ,'2015-01-03 22:02:50.833','545.43')
, (20,'foo27' ,'2015-01-03 22:02:50.935','-2.87')
, (21,'sensor3','2015-01-03 22:02:51.044','6.56');
源表结果：
| id | name | timestamp | value |
|----+-----------+---------------------------+----------|
| 15 | "sensor2" | "2015-01-03 22:02:05.872" | "88.4" |
| 16 | "foo27" | "2015-01-03 22:02:10.887" | "-3.755" |
| 17 | "sensor1" | "2015-01-03 22:02:10.887" | "1.1704" |
| 18 | "foo27" | "2015-01-03 22:02:50.825" | "-1.4" |
| 19 | "bar_18" | "2015-01-03 22:02:50.833" | "545.43" |
| 20 | "foo27" | "2015-01-03 22:02:50.935" | "-2.87" |
| 21 | "sensor3" | "2015-01-03 22:02:51.044" | "6.56" |
期望的最终结果：
| timestamp | sensor1 | sensor2 | sensor3 | foo27 | bar_18 |
|---------------------------+---------+---------+---------+---------+---------|
| "2015-01-03 22:02:05.872" | | 88.4 | | | |
| "2015-01-03 22:02:10.887" | 1.1704 | | | -3.755 | |
| "2015-01-03 22:02:50.825" | | | | -1.4 | |
| "2015-01-03 22:02:50.833" | | | | | 545.43 |
| "2015-01-03 22:02:50.935" | | | | -2.87 | |
| "2015-01-03 22:02:51.044" | | | 6560.00 | | |
使用此：
-- CREATE EXTENSION tablefunc;
SELECT *
FROM
crosstab(
'SELECT
source."timestamp",
source.name,
source.value
FROM
public.source
ORDER BY
1'
,
'SELECT
DISTINCT
source.name
FROM
public.source
ORDER BY
1'
)
AS
(
"timestamp" timestamp without time zone,
"sensor1" character varying(32672),
"sensor2" character varying(32672),
"sensor3" character varying(32672),
"foo27" character varying(32672),
"bar_18" character varying(32672)
)
;
我得到了结果：
| timestamp | sensor1 | sensor2 | sensor3 | foo27 | bar_18 |
|---------------------------+---------+---------+---------+---------+---------|
| "2015-01-03 22:02:05.872" | | | | 88.4 | |
| "2015-01-03 22:02:10.887" | | -3.755 | 1.1704 | | |
| "2015-01-03 22:02:50.825" | | -1.4 | | | |
| "2015-01-03 22:02:50.833" | 545.43 | | | | |
| "2015-01-03 22:02:50.935" | | -2.87 | | | |
| "2015-01-03 22:02:51.044" | | | | | 6.56 |
不幸的是，
答案 0 :(得分：3)
您的查询的工作方式如下：
SELECT * FROM crosstab(
$$SELECT "timestamp", name
, CASE name
WHEN 'sensor3' THEN value::numeric * 1000
-- WHEN 'sensor9' THEN value::numeric * 9000 -- add more ...
ELSE value::numeric END AS value
FROM source
ORDER BY 1, 2$$
,$$SELECT unnest('{bar_18,foo27,sensor1,sensor2,sensor3}'::text[])$$
) AS (
"timestamp" timestamp
, bar_18 numeric
, foo27 numeric
, sensor1 numeric
, sensor2 numeric
, sensor3 numeric);
要将所选列的value相乘，请使用"simple" CASE语句。但是你首先需要转换为numeric type。在示例中使用value::numeric
这引出了一个问题：为什么不将值存储为数字类型？
您需要使用带有两个参数的版本。详细解释：
真正动态交叉制表表接下来不可能，因为SQL要求提前知道结果类型 - 最迟在通话时间。但你可以用多态类型做某事：
答案 1 :(得分：1)
@Erwin：评论说“太长了7128个字符”！无论如何：
你的帖子给了我正确方向的提示，所以非常感谢你， 但特别是在我的情况下，我需要它是真正的动态。目前我有 包含49个不同项目的38886行（=要旋转的列）。
首先回答你和@Jasen的紧急问题： 源表格布局不适合我，我已经很高兴得到这个 数据到RDBMS。如果是我，我总是保存UTC时间戳！但 将数据保存为字符串也是有原因的：它可能包含 各种数据类型，如布尔，整数，浮点数，字符串等。
为了避免让我更加困惑，我创建了一个新的演示数据集，为数据添加前缀 类型（我知道有些讨厌这个！）以避免关键字问题和更改 时间戳（ - >分钟）以获得更好的概述：
-- --------------------------------------------------------------------------
-- Create demo table of given schema and insert arbitrary data
-- --------------------------------------------------------------------------
DROP TABLE IF EXISTS table_source;
CREATE TABLE table_source
(
column_id BIGINT NOT NULL,
column_name CHARACTER VARYING(255),
column_timestamp TIMESTAMP WITHOUT TIME ZONE,
column_value CHARACTER VARYING(32672),
CONSTRAINT table_source_pkey PRIMARY KEY (column_id)
);
INSERT INTO table_source VALUES ( 15,'sensor2','2015-01-03 22:01:05.872','88.4');
INSERT INTO table_source VALUES ( 16,'foo27' ,'2015-01-03 22:02:10.887','-3.755');
INSERT INTO table_source VALUES ( 17,'sensor1','2015-01-03 22:02:10.887','1.1704');
INSERT INTO table_source VALUES ( 18,'foo27' ,'2015-01-03 22:03:50.825','-1.4');
INSERT INTO table_source VALUES ( 19,'bar_18','2015-01-03 22:04:50.833','545.43');
INSERT INTO table_source VALUES ( 20,'foo27' ,'2015-01-03 22:05:50.935','-2.87');
INSERT INTO table_source VALUES ( 21,'seNSor3','2015-01-03 22:06:51.044','6.56');
SELECT * FROM table_source;
此外，根据@ Erwin的建议，我已经创建了一个视图 转换数据类型。这有一个很好的功能，除了快速，只有 为已知项添加必需的转换，但不影响其他（新） 项目
-- --------------------------------------------------------------------------
-- Create view to process source data
-- --------------------------------------------------------------------------
DROP VIEW IF EXISTS view_source_processed;
CREATE VIEW
view_source_processed
AS
SELECT
column_timestamp,
column_name,
CASE LOWER( column_name)
WHEN LOWER( 'sensor3') THEN CAST( column_value AS DOUBLE PRECISION) * 1000.0
ELSE CAST( column_value AS DOUBLE PRECISION)
END AS column_value
FROM
table_source
;
SELECT * FROM view_source_processed ORDER BY column_timestamp DESC LIMIT 100;
这是整个问题的理想结果：
-- --------------------------------------------------------------------------
-- Desired result:
-- --------------------------------------------------------------------------
/*
| column_timestamp | bar_18 | foo27 | sensor1 | sensor2 | seNSor3 |
|---------------------------+---------+---------+---------+---------+---------|
| "2015-01-03 22:01:05.872" | | | | 88.4 | |
| "2015-01-03 22:02:10.887" | | -3.755 | 1.1704 | | |
| "2015-01-03 22:03:50.825" | | -1.4 | | | |
| "2015-01-03 22:04:50.833" | 545.43 | | | | |
| "2015-01-03 22:05:50.935" | | -2.87 | | | |
| "2015-01-03 22:06:51.044" | | | | | 6560 |
*/
这是@ Erwin的解决方案，采用了新的演示源数据。这是完美的， 只要项目（=要旋转的列）不会改变：
-- --------------------------------------------------------------------------
-- Solution by Erwin, modified for changed demo dataset:
-- http://stackoverflow.com/a/27773730
-- --------------------------------------------------------------------------
SELECT *
FROM
crosstab(
$$
SELECT
column_timestamp,
column_name,
column_value
FROM
view_source_processed
ORDER BY
1, 2
$$
,
$$
SELECT
UNNEST( '{bar_18,foo27,sensor1,sensor2,seNSor3}'::text[])
$$
)
AS
(
column_timestamp timestamp,
bar_18 DOUBLE PRECISION,
foo27 DOUBLE PRECISION,
sensor1 DOUBLE PRECISION,
sensor2 DOUBLE PRECISION,
seNSor3 DOUBLE PRECISION
)
;
在阅读@Erwin提供的链接时，我找到了一个动态SQL示例 由@Clodoaldo Neto记得，我已经这样做了 Transact-SQL的;这是我的尝试：
-- --------------------------------------------------------------------------
-- Dynamic attempt based on:
-- http://stackoverflow.com/a/12989297/131874
-- --------------------------------------------------------------------------
DO $DO$
DECLARE
list_columns TEXT;
BEGIN
DROP TABLE IF EXISTS temp_table_pivot;
list_columns := (
SELECT
string_agg( DISTINCT column_name, ' ' ORDER BY column_name)
FROM
view_source_processed
);
EXECUTE(
FORMAT(
$format_1$
CREATE TEMP TABLE
temp_table_pivot(
column_timestamp TIMESTAMP,
%1$s
)
$format_1$
,
(
REPLACE(
list_columns,
' ',
' DOUBLE PRECISION, '
) || ' DOUBLE PRECISION'
)
)
);
EXECUTE(
FORMAT(
$format_2$
INSERT INTO temp_table_pivot
SELECT
*
FROM crosstab(
$crosstab_1$
SELECT
column_timestamp,
column_name,
column_value
FROM
view_source_processed
ORDER BY
column_timestamp, column_name
$crosstab_1$
,
$crosstab_2$
SELECT DISTINCT
column_name
FROM
view_source_processed
ORDER BY
column_name
$crosstab_2$
)
AS
(
column_timestamp TIMESTAMP,
%1$s
);
$format_2$
,
REPLACE( list_columns, ' ', ' DOUBLE PRECISION, ')
||
' DOUBLE PRECISION'
)
);
END;
$DO$;
SELECT * FROM temp_table_pivot ORDER BY column_timestamp DESC LIMIT 100;
除了将其纳入存储过程之外，出于性能原因，我会 尝试将此方法应用于只插入新值的中间表。 我会让你保持最新！
感谢!!!
L，
PS：不，我不想回答我自己的问题，但“评论” - 字段太小了！