An array element can be accessed via an index; if the array does not contain an element for this index, the NULL value is returned, as shown in the following example:

CREATE TABLE color(
  color text []
);
INSERT INTO color(color) VALUES ('{red, green}'::text[]);
INSERT INTO color(color) VALUES ('{red}'::text[]);

To confirm that NULL is returned, let's run the following:

car_portal=> SELECT color [3]IS NOT DISTINCT FROM null FROM color;
 ?column? 
----------
 t
 t
(2 rows)

Also, an array can be sliced by providing a lower and upper bound, as follows:

car_portal=> SELECT color [1:2] FROM color;
    color 
-------------
 {red,green}
 {red}
(2 rows)

When updating an array, one could completely replace the array, get a slice, replace an element, or append the array using the || concatenation operator as shown in the below example. The full set of array functions can be found at: https://www.postgresql.org/docs/current/static/functions-array.html-

car_portal=> SELECT ARRAY ['red', 'green'] || '{blue}'::text[] AS append; 
      append 
------------------
 {red,green,blue}
(1 row)

Time: 0,848 ms
car_portal=> UPDATE color SET color[1:2] = '{black, white}';
UPDATE 2
car_portal=> table color ;
     color 
---------------
 {black,white}
 {black,white}
(2 rows)

The array_remove function can be used to remove all the elements that are equal to a certain value, as follows:

car_portal=> SELECT array_remove ('{Hello, Hello, World}'::TEXT[], 'Hello');
 array_remove 
--------------
 {World}
(1 row)

To remove a certain value based on an index, one can use the WITH ORDINALITY clause. So, let's assume that we want to remove the first element of an array; this can be achieved as follows:

car_portal=> SELECT ARRAY(SELECT unnest FROM unnest ('{Hello1, Hello2, World}'::TEXT[]) WITH ordinality WHERE ordinality <> 1);
     array 
----------------
 {Hello2,World}
(1 row)