So far, the goal was to figure out what to index and to blindly apply an index on this column or on a group of columns. There is one assumption, however, that we have silently accepted to make this work. Up to now, we have been working on the assumption that the order in which data has to be sorted is a somewhat fixed constant. In reality, this assumption might not hold true. Sure, numbers will always be in the same order, but other kinds of data will most likely not have a predefined, fixed sort order.
To prove my point, I have compiled a real-world example. Take a look at the following two records:
1118 09 08 78
2345 01 05 77
My question now is: are those two rows ordered properly? They might because one comes before another. However, this is wrong because those two rows do have some hidden semantics. What you see here is two Austrian social security numbers. 09 08 78 actually means...