In article <59410.193.243.134.6.1064668289.squirrel@www.defero.se>,
"Rasmus Aveskogh" <rasmus@defero.se> writes:
> Hi,
> Since I went from Oracle to PostgreSQL I've been missing the "invisable"
> column 'rownum'. I often used it to lower the granularity of my data.
> For example, say I have a large table containing some sort of statistical
> data and want to plot a graph using it.
> If the graph is 600 pixels wide I might as well lower the granularity of
> my incoming data to 600 measure points before plotting.
> In Oracle I used to do this by using the modulus operator on the rownum
> column as a restriction.
> SELECT <column> FROM <table> WHERE mod(rownum, 5) = 0;
> The query above would give me every fifth row of the original result set
> and would save me from sending the data over my database connection and do
> the lowering of the granularity in the application.
> I have two questions, one dependent on the answer on the other one..
> 1) Is it possible to achieve this any other _easy_ way?
You could fake a rownum by means of a sequence:
CREATE SEQUENCE tmpseq;
SELECT <column>
FROM ( SELECT nextval ('tmpseq') AS rownum, <column> FROM <table> ) AS <table>_with_rownum
WHERE rownum % 5 = 0;
DROP SEQUENCE tmpseq;
