example on how to use postgresql to find the biggest prefix from content at a table

prefix_function.sql

CREATE OR REPLACE FUNCTION public.prefixes(character varying) RETURNS character varying[]
   LANGUAGE sql IMMUTABLE
   AS $_$
SELECT ARRAY(SELECT substring($1 FROM 1 FOR i)
                FROM generate_series(1, GREATEST(length($1))) g(i))::varchar[];
$_$

SELECT MAX(prefix) FROM MY_TABLE WHERE prefix=ANY(content);