Re: [GENERAL] Seamless replacement to MySQL's GROUP_CONCAT function...

Tue, 06 Aug 2013 09:42:30 -0700

A (final?) version using COALESCE (<grin>It wasn't too long to post at the blog now</grin>; I am also posting here for belt and suspenders reasons...):

-- group_concat.sql

-- permutation of GROUP_CONCAT parameter types with delimiter parameter furnished:
CREATE OR REPLACE
FUNCTION GROUP_CONCAT_ATOM(column1 TEXT, column2 TEXT, delimiter TEXT)
         RETURNS TEXT AS $$
BEGIN
RETURN COALESCE(column1||delimiter||column2, column2, column1);
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE
FUNCTION GROUP_CONCAT_ATOM(column1 TEXT, column2 INT8, delimiter TEXT)
         RETURNS TEXT AS $$
BEGIN
RETURN COALESCE(column1||delimiter||CAST(column2 AS TEXT), CAST(column2 AS TEXT), column1);
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE
FUNCTION GROUP_CONCAT_ATOM(column1 INT8, column2 TEXT, delimiter TEXT)
         RETURNS TEXT AS $$
BEGIN
RETURN COALESCE(CAST(column1 AS TEXT)||delimiter||column2, column2, CAST(column1 AS TEXT));
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE
FUNCTION GROUP_CONCAT_ATOM(column1 INT8, column2 INT8, delimiter TEXT)
         RETURNS TEXT AS $$
BEGIN
RETURN COALESCE(CAST(column1 AS TEXT)||delimiter||CAST(column2 AS TEXT), CAST(column2 AS TEXT), CAST(column1 AS TEXT));
END;
$$ LANGUAGE plpgsql;

-- permutation of function arguments without delimiter furnished:
CREATE OR REPLACE
FUNCTION GROUP_CONCAT_ATOM(column1 TEXT, column2 TEXT) -- delimiter=','
         RETURNS TEXT AS $$
BEGIN
RETURN COALESCE(column1||','||column2, column2, column1);
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE
FUNCTION GROUP_CONCAT_ATOM(column1 INT8, column2 INT8) -- delimiter=','
         RETURNS TEXT AS $$
BEGIN
RETURN COALESCE(CAST(column1 AS TEXT)||','||CAST(column2 AS TEXT), CAST(column2 AS TEXT), CAST(column1 AS TEXT));
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE
FUNCTION GROUP_CONCAT_ATOM(column1 INT8, column2 TEXT) -- delimiter=','
         RETURNS TEXT AS $$
BEGIN
RETURN COALESCE(CAST(column1 AS TEXT)||','||column2, column2, CAST(column1 AS TEXT));
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE
FUNCTION GROUP_CONCAT_ATOM(column1 TEXT, column2 INT8) -- delimiter=','
         RETURNS TEXT AS $$
BEGIN
RETURN COALESCE(column1||','||CAST(column2 AS TEXT), CAST(column2 AS TEXT), column1);
END;
$$ LANGUAGE plpgsql;

-- aggregates for all parameter types with delimiter:
DROP AGGREGATE IF EXISTS GROUP_CONCAT(TEXT, TEXT); -- column, delimiter
CREATE AGGREGATE GROUP_CONCAT(TEXT, TEXT) -- column, delimiter
                 (SFUNC=GROUP_CONCAT_ATOM,
                  STYPE=TEXT
                 );

DROP AGGREGATE IF EXISTS GROUP_CONCAT(INT8, TEXT); -- column, delimiter
CREATE AGGREGATE GROUP_CONCAT(INT8, TEXT) -- column
                 (SFUNC=GROUP_CONCAT_ATOM,
                  STYPE=TEXT
                 );

-- aggregates for all parameter types without the optional delimiter:
DROP AGGREGATE IF EXISTS GROUP_CONCAT(TEXT); -- column, delimiter=','
CREATE AGGREGATE GROUP_CONCAT(TEXT) -- column, delimiter=','
                 (SFUNC=GROUP_CONCAT_ATOM,
                  STYPE=TEXT
                 );

DROP AGGREGATE IF EXISTS GROUP_CONCAT(INT8); -- column, delimiter=','
CREATE AGGREGATE GROUP_CONCAT(INT8) -- column, delimiter=','
                 (SFUNC=GROUP_CONCAT_ATOM,
                  STYPE=TEXT
                 );

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