first-last-agg 0.1.4

Synopsis

% CREATE EXTENSION first_last_agg;
CREATE EXTENSION

% SELECT last(x order by y) FROM (VALUES (1, 3), (2, 1), (3, 2)) AS v(x, y);
 last 
------
    1

% SELECT first(x order by y) FROM (VALUES (1, 3), (2, 1), (3, 2)) AS v(x, y);
 first  
-------
     2

Description

This library contains two simple aggregate functions, first and last, operating on any element type. They return the first or the last value of the aggregated group, respectively.

It is useful with aggregates with order by, for easily taking one element from an aggregate group when you don't really care which do you get and for emulating a similar functionality from Oracle.

Author

Jan Urbański, based on code from the PostgreSQL wiki, specifically on the SQL definitions of first and last taken from there.