x² + y² = r² (r – radius)

First you need to create a query/view, based on a square around the circle.

Xmin = X – r

Xmax = X + r

Ymin = Y – r

Ymax = Y + r

This reduces number of rows we need to calculate.

SELECT *

FROM myTable

WHERE (

Xmin <= xCord and xCord <= Xmax

and

Ymin <= yCord and yCord <= Ymax

)

We have a point P(x, y) and radius (r) as criteria

For each query/view row we need to calculate:

(xCord - Px)² + (yCord – Py) ² <= r²

Rows that satisfy the formula above are inside the circle.