Convert Clarion date values from 5 digit integers to DATE types in Postgresql with a custom function

PostgreSQL Clarion date conversion.plsql

# Convert Clarion date values from 5 digit integers to DATE types in Postgresql with a custom function


\d inv
                         Table "public.inv"
   Column   |     Type      |                    Modifiers
------------+---------------+--------------------------------------------------
 create_dt  | integer       |



select create_dt from inv;
 create_dt
-----------
     75864
     74575
     76842
     76842
     75227
     75227
     76700



CREATE OR REPLACE FUNCTION declarion(int) RETURNS date
    AS  $$ select (concat($1, ' days')::interval + date('1800-12-28'))::date; $$
    LANGUAGE SQL
    IMMUTABLE
    RETURNS NULL ON NULL INPUT;


select declarion(create_dt) as create_dt from inv;



 create_dt
------------
 2008-09-12
 2005-03-03
 2011-05-18
 2011-05-18
 2006-12-15
 2006-12-15
 2010-12-27