Attempting to write PostgreSQL 9.0 function

Question

I am attempting to write a function in PostgreSQL 9.0. This will eventually be used in a new aggregate function, but one step at a time. Here is what I have so far:

create or replace function encstate(text,text) returns text as $$
DECLARE
  oldstate alias for $1;
  arg alias for $2;
BEGIN
IF length(oldstate)>0 then
  select 'Encrypted';
else if
  select '';
end if;
END; 
$$ language sql strict immutable;

(I know I'm not yet using the $2 argument.)

The result is:

ERROR:  syntax error at or near "alias"
LINE 3:   oldstate alias for $1;

When I remove the DECLARE block and just refer to the arguments as $1 etc in the body, the result is:

ERROR:  syntax error at or near "if"
LINE 3:   if length($1)>0 then

As far as I can tell, what I have matches examples found on the web, except I could find no examples of functions with an if-statement, so I have no idea what I'm doing wrong. Any help would be appreciated.

Answer 1

If you want a SQL function:

create or replace function encstate(text, text) returns text as $$
select case
    when length($1) > 0 then 'Encrypted'
    else ''
    end
;
$$ language sql strict immutable;

SQL has no variables or control structures as it is not procedural, it is declarative. If you want procedural features then use a plpgsql function:

create or replace function encstate(text, text) returns text as $$
DECLARE
    oldstate alias for $1;
    arg alias for $2;
BEGIN
    IF length(oldstate) > 0 then
        return 'Encrypted';
    else
        return '';
    end if;
END; 
$$ language plpgsql strict immutable;