Re: First Aggregate Funtion?

On Mon, Jul 20, 2015 at 8:40 AM, sudalai  wrote:
>
>>I don't think so, because arrays can contain duplicates.
>
>    I just add two element to the array.  One for INITCOND value NULL, second
> for first row value.
> So Array size is always 2.  So no duplicates.
>
>>rhaas=# select coalesce(first(x.column1), 'wrong') from (values
>>(null), ('correct')) x;
>  >coalesce
>>----------
>> wrong
>>(1 row)
> It works correct..
> I didn't said it returns, first non-null value for a column  from aggregate
> window.
>  I said my implementation returns first row value  for a column.
> Here first row element is "null ", hence it returns null.
>
>
> check this....
> db=# select
> db-# coalesce(first(x.column1),'null') as col1 ,
> db-# coalesce(first(x.column2),'null') as col2,
> db-#  coalesce(first(x.column3),'null') as col3
> db-# from (values (null,'abc',null), ('correct','wrong','notsure'),
> ('second','second1','second3')) x
> db-# ;
>  col1 | col2 | col3
> ------+------+------
>  null | abc  | null
> (1 row)
>
> Its work correct. It returns first row value for a column.

I was able to get ~45% runtime reduction by simply converting
"two_value_holder" from sql to plpgsql.   SQL functions (unlike
pl/pgsql) are parsed and planned every time they are run unless they
are inlined.  Our aggregation API unfortunately is a hard fence
against inlining; solving this is a major optimization target IMO.

merlin