PIVOT VIEW using PostgreSQL

@Erwin: It said "too long by 7128 characters" for a comment! Anyway:

Your post gave me the hints for the right direction, so thank you very much, but particularly in my case I need it be truly dynamic. Currently I've got 38886 rows with 49 different items (= columns to be pivoted).

To first answer yours and @Jasen's urgent question: The source table layout is not up to me, I'm already very happy to get this data into an RDBMS. If it were to me, I'd always save UTC-timestamps! But there's also a reason for having the data saved as strings: it may contain various data types, like boolean, integer, float, string etc.

To avoid confusing me further I created a new demo dataset, prefixing the data type (I know some hate this!) to avoid problems with keywords and changing the timestamp (--> minutes) for better overview:

--  --------------------------------------------------------------------------
--  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;

Furthermore based on @Erwin's suggestions I created a view which already converts the data type. This has the nice feature, beside being fast, to only add required transformations for known items, but not impacting other (new) items.

--  --------------------------------------------------------------------------
--  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;

This is the desired result of the whole question:

--  --------------------------------------------------------------------------
--  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 |
*/

This is @Erwin's solution, adopted to the new demo source data. It's perfect, as long as the items (= columns to be pivoted) doesn't change:

--  --------------------------------------------------------------------------
--  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
        )
    ;

When reading through the links @Erwin provided, I found a Dynamic SQL example by @Clodoaldo Neto and remembered, that I had already done it this way in Transact-SQL; this is my attempt:

--  --------------------------------------------------------------------------
--  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;

Beside getting this into a stored procedure, I will, for performance reasons, try to adopt this to an intermediate table where only new values are inserted. I'll keep you up-to-date!

Thanks!!!

L.

PS: NO, I don't want to answer my own question, but the "comment"-field is too small!