Working with the SQLite-Database - Cursors

Java:publicclassDataBaseWork extendsListActivity {

privatefinalStringMY_DATABASE_NAME = "myCoolUserDB";
privatefinalStringMY_DATABASE_TABLE = "t_Users";

/** Called when the activity is first created. */
@Override
publicvoidonCreate (Bundle icicle ){
super. onCreate(icicle );
/* Will hold the 'Output' we want to display at the end. */
ArrayListresults = newArrayList ();

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,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. */
Cursorc = 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 thegetColumnIndex(String);-method of the Cursor:
Java:/* Get the indices of the Columns we will need */
intfirstNameColumn = c. getColumnIndex("FirstName");
intageColumn = c. getColumnIndex("Age");

/* Check if our result was valid. */
if(c != null){
/* Check if at least one Result was returned. */
if(c. first()){
inti = 0;
/* Loop through all Results */
do{
i++;
/* Retrieve the values of the Entry
* the Cursor is pointing to. */
StringfirstName = c. getString(firstNameColumn );
intage = 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*/
StringageColumName = 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(FileNotFoundExceptione ){
}finally{
if(myDB != null)
myDB. close();
}
8.)In the end,display our Entries:
Java:this. setListAdapter(newArrayAdapter (this,
android. R. layout. simple_list_item_1_small,results ));
}
}

（编辑：李大同）

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What you learn:You will learn how tocreatedatabases andtables,insertandquerydatasets in the Android-built-inSQLite-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: Create a DataBase(generally this is done just once) Open the DataBase Create a Table(generally this is done just once) Insert some Datasets Query for some Datasets 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 !).