After a table is created with its column and datatypes, it is almost ready to use. The primary columns for data linking are done, but it is not quite ready as defined by a DBA. Instead, an index can be created to speed up SQL queries and act as special lookup tables that SQLite will use as a way of getting information faster.
An index has a data pointer, which will quickly reference the data and bring it back, thus making access quicker without much overhead generally. By definition, indexes do have an overhead in their own right, but the overheads of the index are dwarfed by the performance and efficiency gained. This could be useful for mobile applications because of their limited resource and network access.
A database index as an example is similar to the one located in a book, where you can find what you want because you know what it is, and just opens the book to right page, after reading the index.
The index is slow on data input but fast on the SELECT
queries, with or without...