R scatter plot from SQL

CREATE OR REPLACE FUNCTION r_scatter(title text, sql text)
  RETURNS text AS
$BODY$
str <- pg.spi.exec (sql);
pdf('/tmp/scatter_plot.pdf');
plot(str,main=title,cex=0.3, pch=20,col=rgb(255,0,0,2,maxColorValue=255),ylim=c(0,100));
dev.off();
print('done');
$BODY$
  LANGUAGE 'plr' VOLATILE;