Improving PL/pgSQL function - postgresql

Question

I just finished writing my first PLSQL function. Here what it does.
The SQL function attempt to reset the duplicate timestamp to NULL.
From table call_records find all timestamp that are duplicated.(using group by)
loop through each timestamp.Find all record with same timestamp (times-1, so that only 1 record for a given times is present)
From all the records found in step 2 update the timestamp to NULL
Here how the SQL function looks like.
CREATE OR REPLACE FUNCTION nullify() RETURNS INTEGER AS $$
DECLARE
T call_records.timestamp%TYPE;
-- Not sure why row_type does not work
-- R call_records%ROWTYPE;
S integer;
CRNS bigint[];
TMPS bigint[];
sql_stmt varchar = '';
BEGIN
FOR T,S IN (select timestamp,count(timestamp) as times from call_records where timestamp IS NOT NULL group by timestamp having count(timestamp) > 1)
LOOP
sql_stmt := format('SELECT ARRAY(select plain_crn from call_records where timestamp=%s limit %s)',T,S-1);
EXECUTE sql_stmt INTO TMPS;
CRNS := array_cat(CRNS,TMPS);
END LOOP;
sql_stmt = format('update call_records set timestamp=null where plain_crn in (%s)',array_to_string(CRNS,','));
RAISE NOTICE '%',sql_stmt;
EXECUTE sql_stmt ;
RETURN 1;
END
$$ LANGUAGE plpgsql;
Help me understand more PL/pgSQL language my suggesting me how it can be done better.
#a_horse_with_no_name: Here how the DB structure looks like
\d+ call_records;
id integer primary key
plain_crn bigint
timestamp bigint
efd integer default 0
id | efd | plain_crn | timestamp
----------+------------+------------+-----------
1 | 2016062936 | 8777444059 | 14688250050095
2 | 2016062940 | 8777444080 | 14688250050095
3 | 2016063012 | 8880000000 | 14688250050020
4 | 2016043011 | 8000000000 | 14688240012012
5 | 2016013011 | 8000000001 | 14688250050020
6 | 2016022011 | 8440000001 |
Now,
select timestamp,count(timestamp) as times from call_records where timestamp IS NOT NULL group by timestamp having count(timestamp) > 1
timestamp | count
-----------------+-----------
14688250050095 | 2
14688250050020 | 2
All that I want is to update the duplicate timestamp to null so that only one of them record has the given timestamp.
In short the above query should return result like this
select timestamp,count(timestamp) as times from call_records where timestamp IS NOT NULL group by timestamp;
timestamp | count
-----------------+-----------
14688250050095 | 1
14688250050020 | 1

Answer 1

You can use array variables directly (filter with predicate =ANY() - using dynamic SQL is wrong for this purpose:
postgres=# DO $$
DECLARE x int[] = '{1,2,3}';
result int[];
BEGIN
SELECT array_agg(v)
FROM generate_series(1,10) g(v)
WHERE v = ANY(x)
INTO result;
RAISE NOTICE 'result is: %', result;
END;
$$;
NOTICE: result is: {1,2,3}
DO
Next - this is typical void function - it doesn't return any interesting. Usually these functions returns nothing when all is ok or raises exception. The returning 1 RETURN 1 is useless.
CREATE OR REPLACE FUNCTION foo(par int)
RETURNS void AS $$
BEGIN
IF EXISTS(SELECT * FROM footab WHERE id = par)
THEN
...
ELSE
RAISE EXCEPTION 'Missing data for parameter: %', par;
END IF;
END;
$$ LANGUAGE plpgsql;