If this is for an application you're building for browsers, use Leaflet (easy, but not as flexible) or OpenLayers (more flexible, more complicated). Tehre should be database libraries, though I've typically interacted with m database through an API I developed instead of direct from the browser. Cesium exists as well, but that is a resource hog.

IF you're playing around on a local machine, R and Python have sql interfaces that can let you load the data for whatever local processing you want.

You can connect to SQL databases from R, or almost any visualisation or GIS software. Not sure what you mean by 'best'?

I should have been more clear and said "using SQL only without R or python". This is for internal BI use, not for product development.

There's a basic map display in ssms if I recall correctly. But otherwise you can generate a map with something like Tableau. Less of a learning curve than R.

PostGIS.