Just because a result is unexpected does not mean its an incorrect result. No postgresql follows the order of operations as expected.

Now looking at the 2 For loops the First does not have a where clause and the Second has a Where not null this could be the cause of the problem.

Another note you don't need to do this in nested For loops it can be done in a single select statement using nested queries or by using a join clause

Example of a Left Join

Select period, id, 
	(col2-avgResults.col2)/AvgResults.dev_col2, 
	(col1 - AvgResults.col1) / AvgResults.dev_col1 
FROM scheme.table,
Left Join 
		(SELECT period, AVG(col1) AS avg_col1, 
			STDDEV(col1) AS
			dev_col1, AVG(col2) AS avg_col2, 
			STDDEV(col2) AS dev_col2 
	FROM scheme.table
	GROUP BY period 
	Where col1 is not null ) AvgResults 
On AvgResults.period = scheme.table.period

WHERE col1
IS NOT NULL

Assuming i don't have any typos this should give you the results you are looking for and be faster.  

You can throw in a Case statement in the select  testing for grav to limit the result down and speed things up to a single column and do the update that why.

jc_mich wrote:

Hi all!

I'm developing an algorithm with PL/PGSQL using statistical operations from
a table. I have several differences between expected results and the results
generated by the function. 

I want to know if there are differences in arithmetic operation sintax or if
there's any special arithmetical operators precedence between pl/pgsql and
other languages.

My code looks like this:

FOR iterator1 IN SELECT period, AVG(col1) AS avg_col1, STDDEV(col1) AS
dev_col1, AVG(col2) AS avg_col2, STDDEV(col2) AS dev_col2 FROM scheme.table
GROUP BY period ORDER BY period LOOP
	FOR iterator2 IN SELECT period, id, col2, col1 FROM scheme.table WHERE col1
IS NOT NULL LOOP
		IF grav = 0 THEN
			_standata := (iterator2.col1 - iterator1.avg_col1) / iterator1.dev_col1;
			ELSE
				_standata := (iterator2.col2 - iterator1.avg_col2) / iterator1.dev_col2;
		END IF;
		UPDATE scheme.table SET standata = _standata WHERE id = iterator2.id AND
period=iterator2.period;
		_standata := 0.0;
	END LOOP;
END LOOP;

Thanks!