SQL Android

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(); } }

最终结果

05-28 10:00:11.618 16802-16802/? D/MainActivity: onCreate: lisi 38 22.22 05-28 10:00:11.618 16802-16802/? D/MainActivity: onCreate: wangwu 48 44.44