Android入门：SQLite

一、SQLite介绍

SQLite是一个小型的内嵌于Android的数据库；我们不需要引入驱动即可访问它；

SQLite可视化工具：SQLite Expert Professional 3；

二、Android访问SQLite

主要步骤：

(1)创建某个类继承SQLiteOpenHelper,并重写

-- 带Context参数的构造函数; //用来创建数据库

-- onCreate(SQLiteDatabase db); //在创建数据库时调用

-- onUpgrade(SQLiteDatabase db,int old,int newversion); //数据库版本更改时调用

(2)创建数据库：SQLiteDatabase db = helper.getWritableDatabase();

(3)SQL语句：db.execSQL(String sql);

具体模板代码如下：

package org.xiazdong.db.util; import android.content.Context; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import android.util.Log; public class DatabaseHelper extends SQLiteOpenHelper{ private static final String TAG = "DatabaseHelper"; private static int VERSION = 1; public DatabaseHelper(Context context) { super(context, "test.db", null, VERSION); } @Override public void onCreate(SQLiteDatabase db) { db.execSQL("create table 语句"); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { Log.i(TAG, "版本更新..."); } }

当创建数据库时，database存放在/data/data/package/databases 目录中；

1.打开数据库

SQLiteDatabase db = helper.getWritableDatabase();

SQLiteDatabase db = helper.getReadableDatabase(); //此函数内部其实也调用了getWritableDatabase()函数，即调用了此函数，也可以写数据

2.insert语句

(1)db.execSQL("insert into person(name,age) values(?,?)",new Object[]{"xiazdong",20});

(2)

ContentValues values = new ContentValues(); values.put("name","xiazdong"); values.put("age",20); db.insert("tablename",null,values);

3.delete语句

(1)db.execSQL("delete from person where id=?",new Object[]{id});

(2)db.delete("tablename","id=?",new String[]{id+""});

4.update语句

(1)

db.exeSQL("update person set age=? where name=?",new Object[]{30,"xiazdong"});

(2)

ContentValues values = new ContentValues(); values.put("age",30);/*set子句*/ db.update("tablename",values,"name=?"/*where子句*/,new String[]{"xiazdong"}/*where子句参数*/);

5.query语句

(1)

Cursor cursor = db.rawQuery("select * from person where name=?",new Object[]{"xiazdong"}); while(cursor.moveToNext()){ //int index = cursor.getColumnIndex(String name);//根据name获得索引 //String name = cursor.getString(int index); //根据索引获得值 String name = cursor.getString(cursor.getColumnIndex("name")); }

(2)

Cursor cursor = db.query("tablename",null /*表示select * */,"name=?" /*where语句*/,new String[]{"xiazdong"},null /*group by 语句*/,null /*having 语句*/,null /*order by语句*/,null /*limit 语句*/);

6.分页语句

Cursor cursor = db.rawQuery("select * from person limit ?,?",new Object[]{5,5}); //第一个5表示跳过5条记录，下一个5为查询结果的记录个数

while(cursor.moveToNext()){

String name = cursor.getString(cursor.getColumnIndex("name"));

}

7.获得记录个数语句

(1)

Cursor cursor = db.rawQuery("select count(*) from person", null); cursor.moveToFirst(); int count = cursor.getInt(0);

(2)

db.query("person",new String[]{"count(*)"},null,null,null,null,null,null);

三、事务操作

模板代码如下：

db.beginTransaction(); try{ //事务操作 db.setTransactionSuccessful();//此句必须要有，不然db.endTransaction()默认为回滚 } finally{ db.endTransaction(); }