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();
}