i remember getting rejected at the screening stage because i was not able to explain how an sql index works (i'm not a database guy although many people would think this is general knowledge). The next job i got was to build an r-tree for goespatial querying purposes into a database engine. i knew exactly what r-trees and b-trees were, i was exceptionally good with algorithms, but i had no idea what an sql index was. for me it was very ironic and i had since refused to go through tech interviews.