Update database table
Yes you can do that. The easiest way to do if your amount of rows is relatively small is:

update vertex set name = 'CCCC' 
where latitude between 6.9271786 * 0.99 and 6.9271786 * 1.01 and 
      longitude between 79.86224300000006 * 0.99 and 79.86224300000006 * 1.01;


With of course setting your threshold to the right level. The above example assumes 1% which is huge in terms of geo coordinates but you get the idea. 

Since MySQL can only use one column for range queries from a composite key having a combined index won't help but separate index on latitude and longitude will. Then MySQL can choose the one which is more distinctive for the specific case.

create index lat_idx on vertex (latitude);
create index lat_idx on vertex (longitude);


For further optimizations if necessary you can look into spatial indexes (you haven't mentioned which MySQL version and engine you're using).

Also you can geohash the coordinates into a single numerical column and have proximity match on that then filter by the coordinates which I use on bigger database and works like a charm.

https://en.wikipedia.org/wiki/Z-order_curve
https://en.wikipedia.org/wiki/Geohash