[GRASS5] Re: intersect sites with polygons?

[Radim Blazek]

On Friday 05 July 2002 12:39 pm, Christoph Simon wrote:
> The classic SQL example for an aggregate functin is:
>
> 	select max (val) from tab where ...;
>
> this will return just one row, so it's not going to be typical as an
> attribute. 

Select object with category with max value? Not frequent, but say that wee 
want see tha last added feature. Should be possible in this way:
where cat = (select max (cat) from tbl); 

> OTOH, SQL generally and Postgres in particular allows to
> write SQL and C-language based functions, which can do more or less
> everything: Someone might have a map associated with one or more
> tables and one column for each set of climate data measured. This is
> the point, where she could experiment with different algorithms to
> predict future values, compare it to already known ones and compute an
> index of quality of prediction which would be displayed in the map.

Example of SQL statement for this?

> One thing I use pretty frequently, which is not an aggregate function
> but which also requires access to the first part are more or less
> simple arithmetic operations;
>
> 	select inches * 25.4 AS milims from...

Yes, but it does not return list of categories, i guess?

Radim