Dynamische Postgres-Spaltenüberschriften (aus einer anderen Tabelle)

basierend auf der Antwort dynamische Postgres-Spaltenüberschriften (aus einer anderen Tabelle) (die Arbeit von Eric Vallabh Minikel) Ich habe die Funktion verbessert, um flexibler und bequemer zu sein. Ich denke, es könnte auch für andere nützlich sein, zumal es nur auf pg/plsql angewiesen ist und keine Installation von Erweiterungen erfordert, wie es andere Ableitungen von Erics Work (d. H. Plpython) tun. Getestet mit 9.3.5, sollte aber auch mindestens bis 9.2 funktionieren.

Verbesserungen:

• Umgang mit Pivot-Spaltennamen, die Leerzeichen enthalten
• mit mehrzeiligen Kopfspalten umgehen
• Aggregierungsfunktion in Pivot-Zelle sowie nicht aggregierte Pivot-Zelle behandeln (letzter Parameter könnte 'sum(cellval)' oder 'cellval' sein, falls die zugrunde liegende Tabelle/Ansicht bereits Aggregation durchführt)
• Datentyp der Pivot-Zelle automatisch erkennen (muss nicht mehr an die Funktion übergeben werden)

Verwendung:

SELECT get_crosstab_statement('table_to_pivot', ARRAY['rowname' [, <other_row_header_columns_as_well>], 'colname', 'max(cellval)');

Code:

CREATE OR REPLACE FUNCTION get_crosstab_statement(tablename character varying, row_header_columns character varying[], pivot_headers_column character varying, pivot_values character varying)
  RETURNS character varying AS
$BODY$
--returns the sql statement to use for pivoting the table
--based on: http://www.cureffi.org/2013/03/19/automatically-creating-pivot-table-column-names-in-postgresql/
--based on: https://stackoverflow.com/questions/4104508/postgres-dynamic-column-headers-from-another-table
--based on: http://www.postgresonline.com/journal/categories/24-tablefunc

DECLARE
    arrayname CONSTANT character varying := 'r';

    row_headers_simple character varying;
    row_headers_quoted character varying;
    row_headers_castdown character varying;
    row_headers_castup character varying;
    row_header_count smallint;
    row_header record;

    pivot_values_columnname character varying;
    pivot_values_datatype character varying;
    pivot_headers_definition character varying;
    pivot_headers_simple character varying;

    sql_row_headers character varying;
    sql_pivot_headers character varying;
    sql_crosstab_result character varying;

BEGIN
    -- 1. create row header definitions
    row_headers_simple   :=         array_to_string(row_header_columns, ', ');
    row_headers_quoted   := '''' || array_to_string(row_header_columns, ''', ''') || '''';
    row_headers_castdown :=         array_to_string(row_header_columns, '::text, ') || '::text';

    row_header_count     := 0;
    sql_row_headers      := 'SELECT column_name, data_type
                            FROM information_schema.columns
                            WHERE table_name = ''' || tablename || ''' AND column_name IN (' || row_headers_quoted || ')';
    FOR row_header IN EXECUTE sql_row_headers LOOP
        row_header_count := row_header_count + 1;
        row_headers_castup := COALESCE(row_headers_castup || ', ', '') || arrayname || '[' || row_header_count || ']::' || row_header.data_type || ' AS ' || row_header.column_name;
    END LOOP;

    -- 2. retrieve basic column name in case an aggregate function is used
    SELECT coalesce(substring(pivot_values FROM '.*\((.*)\)'), pivot_values)
    INTO pivot_values_columnname;

    -- 3. retrieve pivot values datatype
    SELECT data_type
    FROM information_schema.columns
    WHERE table_name = tablename AND column_name = pivot_values_columnname
    INTO pivot_values_datatype;

    -- 4. retrieve list of pivot column names.
    sql_pivot_headers := 'SELECT string_agg(DISTINCT quote_ident(' || pivot_headers_column || '), '', '' ORDER BY quote_ident(' || pivot_headers_column || ')) as names, string_agg(DISTINCT quote_ident(' || pivot_headers_column || ') || '' ' || pivot_values_datatype || ''', '', '' ORDER BY quote_ident(' || pivot_headers_column || ') || '' ' || pivot_values_datatype || ''') as definitions FROM ' || tablename || ';';
    EXECUTE sql_pivot_headers INTO pivot_headers_simple, pivot_headers_definition;

    -- 5. set up the crosstab query
    sql_crosstab_result := 'SELECT  ' || replace (row_headers_castup || ', ' || pivot_headers_simple, ', ', ',
        ') || '
FROM    crosstab (
        ''SELECT ARRAY[' || row_headers_castdown || '] AS ' || arrayname || ', ' || pivot_headers_column || ', ' || pivot_values || '
        FROM ' || tablename || '
        GROUP BY ' || row_headers_simple || ', ' || pivot_headers_column || (CASE pivot_values_columnname=pivot_values WHEN true THEN ', ' || pivot_values ELSE '' END) || '
        ORDER BY ' || row_headers_simple || '''
    ,
        ''SELECT DISTINCT ' || pivot_headers_column || '
        FROM ' || tablename || '
        ORDER BY ' || pivot_headers_column || '''
    ) AS newtable (
        ' || arrayname || ' varchar[]' || ',
        ' || replace(pivot_headers_definition, ', ', ',
        ') || '
    );';

    RETURN sql_crosstab_result;
 END

 $BODY$
  LANGUAGE plpgsql STABLE
  COST 100;