Re: Seamless replacement to MySQL's GROUP_CONCAT function...

No luck on posting at that blog; comments are limited to X characters.
Here is the final version with the minor update to the variable names
and comments:

-- 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 $$
BEGIN
IF column1 IS NULL THEN
RETURN column2;
ELSIF column2 IS NULL THEN
RETURN column1;
ELSE
RETURN column1||delimiter||column2;
END IF;
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE
FUNCTION GROUP_CONCAT_ATOM(column1 TEXT, column2 INT8, delimiter TEXT)
RETURNS TEXT AS $$
BEGIN
IF column1 IS NULL THEN
IF column2 IS NULL THEN
RETURN NULL;
ELSE
RETURN CAST(column2 AS TEXT);
END IF;
ELSIF column2 IS NULL THEN
RETURN column1;
ELSE
RETURN column1||delimiter||CAST(column2 AS TEXT);
END IF;
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE
FUNCTION GROUP_CONCAT_ATOM(column1 INT8, column2 TEXT, delimiter TEXT)
RETURNS TEXT AS $$
BEGIN
IF column1 IS NULL THEN
RETURN column2;
ELSIF column2 IS NULL THEN
IF column1 IS NULL THEN
RETURN NULL;
ELSE
RETURN CAST(column1 AS TEXT);
END IF;
ELSE
RETURN CAST(column1 AS TEXT)||delimiter||column2;
END IF;
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE
FUNCTION GROUP_CONCAT_ATOM(column1 INT8, column2 INT8, delimiter TEXT)
RETURNS TEXT AS $$
BEGIN
IF column1 IS NULL THEN
IF column2 IS NULL THEN
RETURN NULL;
ELSE
RETURN CAST(column2 AS TEXT);
END IF;
ELSIF column2 IS NULL THEN
IF column1 IS NULL THEN
RETURN NULL;
ELSE
RETURN CAST(column1 AS TEXT);
END IF;
ELSE
RETURN CAST(column1 AS TEXT)||delimiter||CAST(column2 AS TEXT);
END IF;
END;
$$ LANGUAGE plpgsql;

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

CREATE OR REPLACE
FUNCTION GROUP_CONCAT_ATOM(column1 INT8, column2 INT8) -- delimiter=','
RETURNS TEXT AS $$
BEGIN
IF column1 IS NULL THEN
IF column2 IS NULL THEN
RETURN NULL;
ELSE
RETURN CAST(column2 AS TEXT);
END IF;
ELSIF column2 IS NULL THEN
IF column1 IS NULL THEN
RETURN NULL;
ELSE
RETURN CAST(column1 AS TEXT);
END IF;
ELSE
RETURN CAST(column1 AS TEXT)||','||CAST(column2 AS TEXT);
END IF;
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE
FUNCTION GROUP_CONCAT_ATOM(column1 INT8, column2 TEXT) -- delimiter=','
RETURNS TEXT AS $$
BEGIN
IF column1 IS NULL THEN
RETURN column2;
ELSIF column2 IS NULL THEN
IF column1 IS NULL THEN
RETURN NULL;
ELSE
RETURN CAST(column1 AS TEXT);
END IF;
ELSE
RETURN CAST(column1 AS TEXT)||','||column2;
END IF;
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE
FUNCTION GROUP_CONCAT_ATOM(column1 TEXT, column2 INT8) -- delimiter=','
RETURNS TEXT AS $$
BEGIN
IF column1 IS NULL THEN
IF column2 IS NULL THEN
RETURN NULL;
ELSE
RETURN CAST(column2 AS TEXT);
END IF;
ELSIF column2 IS NULL THEN
RETURN column1;
ELSE
RETURN column1||','||CAST(column2 AS TEXT);
END IF;
END;
$$ 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
);