In this chapter, we started by focusing on the Android OS and by looking at what types of query methods are at your disposal. We saw that there are three well-known ways to interact with the SQLite database, some more 'convenient' than the others, and some more flexible and powerful than the others.

However, we also saw that though each method had its pros and cons, all three query methods could ultimately perform the same kinds of queries, just using different sets of syntax or using different sets of parameters. This is when we moved away from the methods themselves and focused more on the query itself, starting with simple queries, which ranged from the most basic SELECT queries to more involved queries that allowed you to specify specific columns and rows. And later, we talked about more advanced queries, which ranged from ORDERBY and GROUPBY queries to the most complex and involved JOIN statements.

And lastly, being the curious and performance-minded programmers that we are, we spent the last section comparing the speeds of SQL and Java – implementing a variety of queries in both SQL and Java and then running them to look at the respective speeds. We saw that in each case, being able to embed your desired functionality into an SQL query granted you a performance boost when compared to executing that same functionality in Java (in one case it gave us as much as a 16x performance boost). And so, the moral of the story for this section is that when possible, find ways to manipulate your data on the SQL side as opposed to the Java side, as it will help you optimize speed as well as memory usage!

But before moving on, let's take a second to synthesize what we've learned so far. Earlier in Chapter 2, Using a SQLite Database, we learned about implementing SQLite database schemas in your Android application, and just now we learned about all the different features that are built into SQL which ultimately allow you to work with your data in extremely powerful, efficient ways. But now, what if you want to tap into existing data on the user's Android device? Each Android device contains a wealth of data, much of which is available for external applications to query, and so it's important to keep this in mind when developing your application. Furthermore, what if you want to expose your database and schemas to other applications? What if you're building a task list application and you want to allow other applications (perhaps calendar-based applications) to query for the user's existing tasks? All of these things are done through what's called a ContentProvider, and it's in the next two chapters that we flush out this extremely important class in Android.