Find if points are within a circle with given center and radius

Question

We have a point (x,y) and a set of some other points (xi,yi). How can we determine which of (xi,yi) are within a circle with c

Answer 1

I had the same problem to solve inside a plsql procedure. The solution above are completely right and I did the same. But it compromised the performance of my plsql program drastically. Instead of that circle calculation, I used a square. Because it can be done without doing such calculation and in the sql statement itself. It improved the query performance by more than 10x