Query indexing is a mature technique in relational databases. Organizing as tree-like structures, the indexes facilitate data access and speed up query processing. Nevertheless, the construction and modification of the indexes is very expensive and can slow down the database performance. Traditional approaches cover all records equally, even if some records are queried often and some never. To avoid this problem, partially indexing has been introduced. The core idea is to create indexes adaptively and incrementally as a side-product of query processing. In this way, only such records are indexed which take part in the queries. After emerging modern data storage technologies like: flash memory or phase change memory, the new index types appeared. They have been invented to overcome the limitations of such technologies. In this paper, we deal with partially indexing on flash memory. We propose a method which reduces the number of write and erase operations on flash memory during index creation. Due to employing optimization techniques specific for flash memory, the query response time is decreased twice in comparison to the traditional methods. As far as we know, it is the first approach which considers partially indexing on the physical data storage level. Thus, the paper may be the initiation of a new research direction.