Syntax error at or near "(" while calling function - sql

Question

While running this code, I am getting following error:
ERROR: syntax error at or near "(";
error while executing the query(7)
Code:
CREATE OR REPLACE FUNCTION obs_updated_date() RETURNS INTEGER AS $$
DECLARE
i RECORD;
BEGIN
FOR i IN
(SELECT r FROM pg_class
WHERE r LIKE 'abc%1')
LOOP
EXECUTE 'update' || i || 'SET observation_time = xyz + INTERVAL"18 hour"';
END LOOP;
RETURN 1;
END;
$$ LANGUAGE plpgsql;
SELECT obs_updated_date();
DROP FUNCTION obs_updated_date();

Answer 1

The main error are double quotes where you need single quotes for the literal value:
INTERVAL "18 hour"
INTERVAL '18 hour'
But since that's nested in a quoted string I suggest outer dollar quotes:
EXECUTE 'update' || i || $u$SET observation_time = date_added + INTERVAL '18 hour'$u$;
Related:
Insert text with single quotes in PostgreSQL
Better yet, quote the table name properly using format():
EXECUTE format ($u$UPDATE %I SET observation_time = date_added + INTERVAL '18 hour'$u$, i);
And you can't use a record variable like you did. And some more improvements, resulting in:
CREATE OR REPLACE FUNCTION obs_updated_date()
RETURNS int AS
$func$
DECLARE
_tbl regclass;
_ct int := 0;
BEGIN
FOR _tbl IN
SELECT oid
FROM pg_class
WHERE relname LIKE 'traffic%1'
AND relkind = 'r' -- only actual tables
AND relnamespace::regnamespace::text NOT LIKE 'pg_%' -- no system tables
LOOP
EXECUTE format ($u$UPDATE %I SET observation_time = date_added + interval '18 hour'$u$, _tbl);
_ct := _ct + 1;
END LOOP;
RETURN _ct; -- return sth useful: the number of affected tables
END
$func$ LANGUAGE plpgsql;
You don't need a record to begin with. text would do it. Better, yet, use type regclass for the table names, since that automatically adds schema names where required. Else, this might go terribly wrong with table names that are used in multiple schemas.
Table name as a PostgreSQL function parameter
For 1-time use (as indicated by your dangling DROP FUNCTION) consider a DO statement instead of a function:
DO
$do$
DECLARE
_tbl regclass;
_ct int := 0;
BEGIN
...
RAISE NOTICE '% tables updated.', _ct;
END
$do$;

Answer 2

There are three errors in the code:
i is a RECORD, i.e. a whole row of results. Concatenating it to a string implicitly puts ( ) around it, producing update(trafficfoo1)SET .... This is what causes the syntax error. You need to either use i.relname or declare i as TEXT.
There are missing spaces around i in the generated string.
The wrong kind of quotes are used for "18 hour". Double quotes are for identifiers, not strings. '18 hour' (single quotes) work, but in the context of a single-quoted string ' needs to be escaped as '', giving ''18 hour''.
A working version:
CREATE OR REPLACE FUNCTION obs_updated_date() RETURNS INTEGER AS $$
DECLARE
i TEXT;
-- ^^^^
BEGIN
FOR i IN
SELECT relname FROM pg_class
WHERE relname LIKE 'traffic%1'
LOOP
execute 'update ' || i || ' SET observation_time = date_added + INTERVAL''18 hour''';
-- ^ ^ ^^ ^^
END LOOP;
RETURN 1;
END;
$$ LANGUAGE plpgsql;