Added function for merging arrays for task #3892

-- This function returns an array adding some elements and removing others

-- It is used to update recursively groupread and groupwrite properties

CREATE OR REPLACE FUNCTION update_array(input_array VARCHAR[], elements_to_add VARCHAR[], elements_to_remove VARCHAR[]) RETURNS VARCHAR[] AS

$func$

SELECT array_agg(elements) FROM (

    SELECT DISTINCT UNNEST(input_array)

    UNION SELECT DISTINCT UNNEST(elements_to_add)

    EXCEPT SELECT DISTINCT UNNEST(elements_to_remove)

) AS output_values(elements)

$func$ LANGUAGE sql;

SELECT update_array('{"group1","group2"}'::VARCHAR[],'{"group2","group3"}'::VARCHAR[],'{"group1"}'::VARCHAR[]) = '{"group2","group3"}' AS test_passed;