baserat på svar Postgres dynamiska kolumnrubriker (från ett annat bord) (Eric Vallabh Minikels arbete) Jag förbättrade funktionen för att vara mer flexibel och bekväm. Jag tror att det kan vara användbart för andra också, särskilt eftersom det bara är beroende av pg/plsql och inte behöver installera extensions som andra härledningar av erics arbete (dvs plpython) gör. Testet med 9.3.5 men bör också fungera åtminstone ner till 9.2.
Förbättringar:
- hantera pivoterade kolumnnamn som innehåller mellanslag
- hantera flera radrubrikkolumner
- hantera aggregerad funktion i pivotcell såväl som icke-aggregerad pivotcell (sista parametern kan vara 'sum(cellval)' såväl som 'cellval' om den underliggande tabellen/vyn redan gör aggregering)
- Automatisk identifiering av datatyp för pivotcell (du behöver inte skicka den till funktionen längre)
Användning:
SELECT get_crosstab_statement('table_to_pivot', ARRAY['rowname' [, <other_row_header_columns_as_well>], 'colname', 'max(cellval)');
Kod:
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;