How to store x,y graphs: (a) Using x,y columns for each point, or (b) to store the set of points as comma separated strings?
There's a third option: store column 2 and 3 together, so like

X1,Y1,X2,Y2,X3,Y3


If you're absolutely sure you never need to sort or filter on these coordinates, and rely on application logic to create, update and process them, it's fine to store them as a 'blob' in a single column.