validate if a is a valid date (postgresql)

is_valid_date.sql

-- from https://dba.stackexchange.com/a/8835/16235

create function is_valid_date(text) returns boolean language plpgsql immutable as $$
begin
  return case when $1::date is null then false else true end;
exception when others then
  return false;
end;$$;

-- use:
-- select case when is_valid_date(column) then column::date end from table