SQL Android _Android

黄沙百战穿金甲，不破楼兰终不还。这篇文章主要讲述SQL Android相关的知识，希望能为你提供帮助。
SQLite是一款轻量级的关系型数据库，它的运算速度非常快，占用资源很少。
一般有以下几个关键步骤：
1.创建数据库
2.创建表
3.操作：增删改查
4.关闭数据库
5.删除表（非必选）
SQLiteOpenHelper是SQLiteDatabse的一个帮助类，用来管理数据的创建和版本更新。一般的用法是定义一个类继承SQLiteOpenHelper，并实现两个回调方法，OnCreate(SQLiteDatabase db)和onUpgrade(SQLiteDatabse, int oldVersion, int newVersion)来创建和更新数据库。

下面新建类MyDatabaseHelper继承自SQLiteOpenHelper，并创建了表people

public class MyDatabaseHelper extends SQLiteOpenHelper {

public static final String CREATE_PEOPLE = "create table people ("+"id integer primary key autoincrement,"+"name text,"+"age int,"+"price double)";

public MyDatabaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
super(context, name, factory, version);
}

@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
//创建表
sqLiteDatabase.execSQL(CREATE_PEOPLE);
}

@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

//删除旧表重新创建
sqLiteDatabase.execSQL("drop table if exists people");
onCreate(sqLiteDatabase);
}
}

下面采用了两种方式来展示增删改查
第一种：纯SQL语句

public class MainActivity extends AppCompatActivity {

private static final String TAG = "MainActivity";
private MyDatabaseHelper myDatabaseHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

//增加version 来删除之前的表信息
myDatabaseHelper = new MyDatabaseHelper(this,"peopleInfo.db",null,9);
//创建数据库
myDatabaseHelper.getWritableDatabase();

//打开数据库
SQLiteDatabase database = myDatabaseHelper.getWritableDatabase();
//新增zhangsan 18 11.11
//ContentValues values = new ContentValues();
//values.put("name","zhangsan");
//values.put("age",18);
//values.put("price",11.11);
//database.insert("people",null,values);

database.execSQL("insert into people (name,age,price) values(?,?,?)",new String[] {"zhangsan","18","11.11"});

//新增lisi 28 22.22
//values.clear();
//values.put("name","lisi");
//values.put("age",28);
//values.put("price",22.22);
//database.insert("people",null,values);

database.execSQL("insert into people (name,age,price) values(?,?,?)",new String[] {"lisi","28","22.22"});

//新增wangwu 48 44.44
//values.clear();
//values.put("name","wangwu");
//values.put("age",48);
//values.put("price",44.44);
//database.insert("people",null,values);

database.execSQL("insert into people (name,age,price) values(?,?,?)",new String[] {"wangwu","48","44.44"});

//删除zhangsan信息
//database.delete("people","name = ?",new String[] {"zhangsan"});

database.execSQL("delete from people where name = ?",new String[] {"zhangsan"});

//更改lisi age=38
//values.clear();
//values.put("age",38);
//database.update("people",values,"name = ?",new String[] {"lisi"});

database.execSQL("update people set age = ? where name = ? ",new String[] {"38","lisi"});

//查询people表的内容并打印
//Cursor cursor = database.query("people",null,null,null,null,null,null,null);
Cursor cursor = database.rawQuery("select * from people",null);
if (cursor.moveToFirst()){
do{
String name = cursor.getString(cursor.getColumnIndex("name"));
int age = cursor.getInt(cursor.getColumnIndex("age"));
double price = cursor.getDouble(cursor.getColumnIndex("price"));

Log.d(TAG, "onCreate: "+name+" "+age+" "+price);

}while (cursor.moveToNext());

}
cursor.close();

}
}

第二种：android对象方式

public class MainActivity extends AppCompatActivity {

private static final String TAG = "MainActivity";
private MyDatabaseHelper myDatabaseHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

//增加version 来删除之前的表信息
myDatabaseHelper = new MyDatabaseHelper(this,"peopleInfo.db",null,9);
//创建数据库
myDatabaseHelper.getWritableDatabase();

//打开数据库
SQLiteDatabase database = myDatabaseHelper.getWritableDatabase();
//新增zhangsan 18 11.11
ContentValues values = new ContentValues();
values.put("name","zhangsan");
values.put("age",18);
values.put("price",11.11);
database.insert("people",null,values);

//database.execSQL("insert into people (name,age,price) values(?,?,?)",new String[] {"zhangsan","18","11.11"});

//新增lisi 28 22.22
values.clear();
values.put("name","lisi");
values.put("age",28);
values.put("price",22.22);
database.insert("people",null,values);

//database.execSQL("insert into people (name,age,price) values(?,?,?)",new String[] {"lisi","28","22.22"});

//新增wangwu 48 44.44
values.clear();
values.put("name","wangwu");
values.put("age",48);
values.put("price",44.44);
database.insert("people",null,values);

//database.execSQL("insert into people (name,age,price) values(?,?,?)",new String[] {"wangwu","48","44.44"});

//删除zhangsan信息
database.delete("people","name = ?",new String[] {"zhangsan"});

//database.execSQL("delete from people where name = ?",new String[] {"zhangsan"});

//更改lisi age=38
values.clear();
values.put("age",38);
database.update("people",values,"name = ?",new String[] {"lisi"});

//database.execSQL("update people set age = ? where name = ? ",new String[] {"38","lisi"});

//查询people表的内容并打印
Cursor cursor = database.query("people",null,null,null,null,null,null,null);
//Cursor cursor = database.rawQuery("select * from people",null);
if (cursor.moveToFirst()){
do{
String name = cursor.getString(cursor.getColumnIndex("name"));
int age = cursor.getInt(cursor.getColumnIndex("age"));
double price = cursor.getDouble(cursor.getColumnIndex("price"));

Log.d(TAG, "onCreate: "+name+" "+age+" "+price);

}while (cursor.moveToNext());

}
cursor.close();

}
}