ИЗБЕРЕТЕ динамични колони без функции в PostgreSQL

Това, което се опитвате да направите, едва ли е възможно в своята цялост.

Създайте динамичен SQL

Първо, ето какво можете do:plpgsql функция, която създава SQL за такава заявка:

CREATE OR REPLACE FUNCTION f_union_common_col_sql(text, text)
 RETURNS text
AS $function$
DECLARE 
  _cols text;
BEGIN

_cols := string_agg(attname, ', ')
FROM (
    SELECT a.attname
    FROM   pg_attribute a
    WHERE  a.attrelid = $1::regclass::oid
    AND    a.attnum >= 1
    INTERSECT
    SELECT a.attname
    FROM   pg_attribute a
    WHERE  a.attrelid = $2::regclass::oid
    AND    a.attnum >= 1
    ) x;

RETURN 'SELECT ' || _cols || '
FROM   ' || quote_ident($1) || '
UNION
SELECT ' || _cols || '
FROM   ' || quote_ident($1);

END;
$function$  LANGUAGE plpgsql;

COMMENT ON FUNCTION f_union_common_col_sql(text, text) IS 'Create SQL to query all visible columns that two tables have in common.
# Without duplicates. Use UNION ALL if you want to include duplicates.
# Depends on visibility dicatated by search_path
$1 .. table1: optionally schema-qualified, case sensitive!
$2 .. table2: optionally schema-qualified, case sensitive!';

Обаждане:

SELECT f_union_common_col_sql('myschema1.tbl1', 'myschema2.tbl2');

Дава ви пълната заявка. Изпълнете го при второ повикване.

Можете да намерите почти всичко, което използвах тук, в ръководството за функциите на plpgsql .
обобщаваща функция string_agg() беше въведен с PostgreSQL 9.0. В по-стари версии бихте:array_to_string(array_agg(attname), ', ') .

CREATE OR REPLACE FUNCTION f_union_common_col(text, text)
  RETURNS SETOF record AS
$BODY$
DECLARE 
  _cols text;
BEGIN

_cols := string_agg(attname, ', ')
FROM (
    SELECT a.attname
    FROM   pg_attribute a
    WHERE  a.attrelid = $1::regclass::oid
    AND    a.attnum >= 1
    INTERSECT
    SELECT a.attname
    FROM   pg_attribute a
    WHERE  a.attrelid = $2::regclass::oid
    AND    a.attnum >= 1
    ) x;

RETURN QUERY EXECUTE '
SELECT ' || _cols || '
FROM quote_ident($1)
UNION
SELECT ' || _cols || '
FROM quote_ident($2)';

END;
$BODY$
  LANGUAGE plpgsql VOLATILE;

COMMENT ON FUNCTION f_union_common_col(text, text) IS 'Query all visible columns that two tables have in common.
# Without duplicates. Use UNION ALL if you want to include duplicates.
# Depends on visibility dicatated by search_path
# !BUT! you need to specify a column definition list for every call. So, hardly useful.
$1 .. table1 (optionally schema-qualified)
$2 .. table1 (optionally schema-qualified)';

SELECT * from f_union_common_col('myschema1.tbl1', 'myschema2.tbl2')

ERROR:  a column definition list is required for functions returning "record"