in postgres, there currently isnt a function to combine two arrays and remove duplicates - this will do that.

postgres-merge-arrays.sql

CREATE OR REPLACE FUNCTION mergeArrays (a1 ANYARRAY, a2 ANYARRAY) RETURNS ANYARRAY AS $$

	SELECT ARRAY_AGG(x ORDER BY x)
	FROM (
		SELECT DISTINCT UNNEST($1 || $2) AS x
	) s;

$$ LANGUAGE SQL STRICT;

Very nice, thanks!

doesn't seem to work when one of the arrays is empty.

doesn't seem to work when one of the arrays is empty.

It looks like it works to me - an empty array you must define as the kind of data type in the array, but it works.

https://dbfiddle.uk/?rdbms=postgres_9.6&fiddle=ae6385a5b138c262008de6f0b35986e5