May be I gave a wrong example to explain my issue.
Below is a sample query that I have been trying to get the slope and intercept. The inner query basically gives me the time vs capacity, ie. x and y data showing the actuals. Based on the x, y value, I calculate slope and intercept value, as in the outer query.
But it looks like am back to your comment as it mentions I am asking for slope and intercept of a single point. Could you provide me some examples that I can use as a reference. As a reference, I am following similar example as in http://stackoverflow.com/questions/20490756/linear-regression-with-postgres
select x, y, regr_slope(y,x), regr_intercept(y,x) from (
/* doesn't matter */
) i group by x, y order by x asc, y asc
You are grouping on (x, y)
and then passing this single POINT into a function that requires multiple points in order to calculate the slope and intercept of a LINE (i.e., something requiring two points to describe) and are confused why it is giving you NULL...
I have answered your question - you are using the functions incorrectly.
This is operator error, not a bug.
You have already found a reasonably good example of how these functions can be used. Given I have never used them myself I do not have anything better to offer.
