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 staticint VERSION = 1;public DatabaseHelper(Context context) {super(context, "test.db", null, VERSION);}@Overridepublic void onCreate(SQLiteDatabase db) {db.execSQL("create table 语句");}@Overridepublic 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=?",newObject[]{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/*groupby 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();}
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