Working with the SQLite-Database - Cursors

What you learn: You will learn how to create databases and tables, insert and query datasets in the Android-built-in SQLite-DataBase-Server.

Difficulty: 1 of 5 

 Questions/Problems: Simply post below...

What it will look like:

Description:
We'll need to to the following things:

1. Create a DataBase (generally this is done just once)
2. Open the DataBase
3. Create a Table (generally this is done just once)
4. Insert some Datasets
5. Query for some Datasets
6. Close the Database

0.) So lets work it out:
We first do some setup. Declaring the DataBases/Tables we are using as final should always be preferred before typing the name to every single statement. (Changes are a lot easier !).
Java:

public class DataBaseWork extends ListActivity {

private final String MY_DATABASE_NAME = "myCoolUserDB";
private final String MY_DATABASE_TABLE = "t_Users";

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
/* Will hold the 'Output' we want to display at the end. */
ArrayList results = new ArrayList();

1.) So lets create the DataBase:
Java:

SQLiteDatabase myDB = null;
try {
/* Create the Database (no Errors if it already exists) */ 
this.createDatabase(MY_DATABASE_NAME, 1, MODE_PRIVATE, null);

2.) Having created the DataBase we want to open it:
Java:

/* Open the DB and remember it */
myDB = this.openDatabase(MY_DATABASE_NAME, null);

3.) Now we create a simple Table with just four columns:
Java:

/* Create a Table in the Database. */ 
myDB.execSQL("CREATE TABLE IF NOT EXISTS "
+ MY_DATABASE_TABLE
+ " (LastName VARCHAR, FirstName VARCHAR,"
+ " Country VARCHAR, Age INT(3));");

4.) Put two DataSets to the recently created Table:
Java:

/* Add two DataSets to the Table. */
myDB.execSQL("INSERT INTO "
+ MY_DATABASE_TABLE
+ " (LastName, FirstName, Country, Age)"
+ " VALUES ('Gramlich', 'Nicolas', 'Germany', 20);");
myDB.execSQL("INSERT INTO "
+ MY_DATABASE_TABLE
+ " (LastName, FirstName, Country, Age)"
+ " VALUES ('Doe', 'John', 'US', 34);");

5.) Having written some DataSets to the Table, we would want to receive them back somewhen. Thr result of a query is a Cursor that can move over all the results returned by the query. We apply Projection (Just the Specified Columns) and Selection (WHERE ...) to it and a LIMIT. Just as we would do in any other SQL-"Dialect":
Java:

/* Query for some results with Selection and Projection. */
Cursor c = myDB.query("SELECT FirstName,Age" +
" FROM " + MY_DATABASE_TABLE 
+ " WHERE Age > 10 LIMIT 7;",
null);

6.) Now having queried, we retrieve the ColumIndexes of two Columns calling the getColumnIndex(String);-method of the Cursor:
Java:

/* Get the indices of the Columns we will need */
int firstNameColumn = c.getColumnIndex("FirstName");
int ageColumn = c.getColumnIndex("Age");

/* Check if our result was valid. */
if (c != null) {
/* Check if at least one Result was returned. */ 
if (c.first()) {
int i = 0;
/* Loop through all Results */ 
do {
i++;
/* Retrieve the values of the Entry
* the Cursor is pointing to. */
String firstName = c.getString(firstNameColumn);
int age = c.getInt(ageColumn);
/* We can also receive the Name 
* of a Column by its Index.
* Makes no sense, as we already 
* know the Name, but just to shwo we can  */
String ageColumName = c.getColumnName(ageColumn);

/* Add current Entry to results. */
results.add("" + i + ": " + firstName 
+ " (" + ageColumName + ": " + age + ")");
} while (c.next());
}
}

7.) Finally close the DataBase (if it has been opened):
Java:

} catch (FileNotFoundException e) {
} finally {
if (myDB != null)
myDB.close();
}

8.) In the end, display our Entries:
Java:

this.setListAdapter(new ArrayAdapter(this,
android.R.layout.simple_list_item_1_small, results));
}
}