This simple query will always run as a table (or index) scan. How long it takes to complete will depend upon quite a few factors and some of these are variable, such as the current server load, how much of the customer table happens to be in cache, the state of the network between server and clients and how busy the clients are (you're returning and displaying all results, remember). Whilst it's not impossible to obtain some measure of these variables, you should ask yourself if it's a worthwhile exercise to conduct on a query which you know to be poorly written and in need of a little tweaking. Unless of course you're baselining, but that's a different story.