Indexing memory-optimized tables was quite restrictive in the initial version of the In-Memory OLTP engine. However, thus far in this chapter, we have seen that there have been a number of improvements (including adding, removing, and rebuilding indexes), but there are more to come!

It is now possible to define non-unique indexes with NULLable key columns for memory-optimized tables. The NULLability is something that is widely used, and the move towards parity between memory-optimized and disk-based indexes is continued here.

Similarly, it is possible to declare UNIQUE indexes (other than the primary key) for memory-optimized tables.

We will take a deeper look at indexing later on in this chapter in the section titled, Down the index rabbit-hole.