Can we define a GROUP_CONCAT function in PostgreSQL?

Question

I have several lines of SQL code for my legacy database with GROUP_CONCAT statements, as in:

SELECT SUM(age), GROUP_CONCAT(sal) FROM Users;
<         


        

Answer 1

Yes this is possible. Have a look at https://github.com/2ndQuadrant/mysqlcompat/blob/master/sql_bits/aggregate.sql where it's already done, as such:

-- GROUP_CONCAT()
-- Note: only supports the comma separator
-- Note: For DISTINCT and ORDER BY a subquery is required
CREATE OR REPLACE FUNCTION _group_concat(text, text)
RETURNS text AS $$
  SELECT CASE
    WHEN $2 IS NULL THEN $1
    WHEN $1 IS NULL THEN $2
    ELSE $1 operator(pg_catalog.||) ',' operator(pg_catalog.||) $2
  END
$$ IMMUTABLE LANGUAGE SQL;

CREATE AGGREGATE group_concat (
    BASETYPE = text,
    SFUNC = _group_concat,
    STYPE = text
);