android数据库的基本回顾

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本篇主要想回顾一下android数据库的基本使用及几个注意点：

一、在我测试的时候，只要设置了自动了增长的id键，就无法设置其他的字段为主键，或者将id和其他字段一起设置为主键，不知道是硬性的规定还是我SQL建表语句的问题

二、对于自动增长的id键有的书说必须要，有的书说可以不要，我试了一下，都可以，而且没有id时，可以设置多个主键，但是android讲义中说到当使用SimpleCursorAdapter时其对应的数据来源的Cursor中必须有_id这一字段，试了一下确实是这样

三、对于_id这一字段是可以人为改动的，而且后面的没有指定_id的元组貌似会根据前面最大的_id为起点增加

相应的代码如下，当然代码还是很乱

public class MyDatabase extends SQLiteOpenHelper {    final static String CREATE_STU="create table Student(" +            "_id integer primary key autoincrement,"+            "stuno text,"+            "cname text"+            ")";    final static String CREATE_TEA="create table Teacher(" +            "id integer primary key autoincrement,"+            "teano text,"+            "cname text"+            ")";    final static String CREATE_TEST="create table TEST(" +            "test text ,"+            "tname text," +            "primary key(test,tname)"+            ")";    public MyDatabase(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {        super(context, name, factory, version);    }    @Override    public void onCreate(SQLiteDatabase db) {        db.execSQL(CREATE_STU);        db.execSQL(CREATE_TEA);        db.execSQL(CREATE_TEST);    }    @Override    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {        switch (oldVersion){            case 1:            case 2:                //.....作为一种升级的方法        }    }}

活动的测试代码如下

public class MainActivity extends Activity {    MyDatabase database;    final static String DATABASENAME="stutea.db";    TextView textView;    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        database=new MyDatabase(this,DATABASENAME,null,1);        textView=(TextView)findViewById(R.id.text);    }    public void Adddate(View source){        SQLiteDatabase db=database.getWritableDatabase();        ContentValues contentValues=new ContentValues();        contentValues.put("test","1");        contentValues.put("tname", "math");        db.insert("TEST", null, contentValues);        contentValues.clear();        contentValues.put("test", "3");        contentValues.put("tname", "math");        db.insert("TEST", null, contentValues);        contentValues.clear();        contentValues.put("stuno", "1");        contentValues.put("cname", "math");        db.insert("Student", null, contentValues);        contentValues.clear();        contentValues.put("stuno", "2");        contentValues.put("cname", "math");        db.insert("Student", null, contentValues);        contentValues.clear();        contentValues.put("_id", 12);//可以指定_id字段的值        contentValues.put("stuno","3");        contentValues.put("cname","math");        db.insert("Student", null, contentValues);        contentValues.clear();        contentValues.put("stuno", "4");        contentValues.put("cname", "math");        db.insert("Student", null, contentValues);        db.execSQL("insert into Student(stuno,cname) values(?,?)", new String[]{"5", "chinest"});        db.execSQL("insert into Student(stuno,cname) values(?,?)", new String[]{"6", "english"});        db.execSQL("insert into Student(stuno,cname) values(?,?)", new String[]{"7", "biology"});        db.execSQL("insert into Teacher(teano,cname) values(?,?)",new String[]{"12","chinest"});        db.close();    }    public void DeleteData(View Source){        SQLiteDatabase db=database.getWritableDatabase();        db.beginTransaction();//使用事务        int delid=db.delete("Student", "stuno=?", new String[]{"7"});//返回被影响的行数        Toast.makeText(this,"id is "+delid,Toast.LENGTH_SHORT).show();        db.execSQL("delete from Student where stuno like ?", new String[]{"2"});        db.setTransactionSuccessful();//必须使用，否则修改无法启用        db.endTransaction();        textView.append("id is " + delid + "\n");        db.close();    }    public void QueryData(View Source){        SQLiteDatabase db=database.getReadableDatabase();        Cursor cursor=db.rawQuery("select stuno,teano from Student,Teacher where stuno=? and Student.cname=Teacher.cname",                new String[]{"5"});    //    Cursor all=db.rawQuery("select * from Student",null);        Cursor all=db.rawQuery("select * from TEST",null);        Cursor cursor1=db.rawQuery("select * from Student",null);        SimpleCursorAdapter adapter=new SimpleCursorAdapter(this,android.R.layout.simple_expandable_list_item_1,cursor1,new String[]{"stuno"},                new int[]{android.R.id.text1},CursorAdapter.NO_SELECTION);//仅仅为了测试一下        if(cursor.moveToFirst()){            do{              textView.append(cursor.getString(cursor.getColumnIndex("stuno"))+" ");                textView.append(cursor.getString(cursor.getColumnIndex("teano")));            } while(cursor.moveToNext());        }        cursor.close();        if(all.moveToFirst()){            do{ //               textView.append(all.getString(all.getColumnIndex("stuno")));   //             textView.append(""+all.getInt(all.getColumnIndex("_id")));     //           textView.append(all.getString(all.getColumnIndex("cname"))+"\n");                textView.append(all.getString(all.getColumnIndex("test")));                textView.append(all.getString(all.getColumnIndex("tname"))+"\n");            } while(all.moveToNext());            all.close();        }        db.close();    }    public void AlertData(View Source){        SQLiteDatabase db = database.getWritableDatabase();  //      db.execSQL("update Student set stuno=? where stuno=?",new String[]{"19","2"});        ContentValues contentValues=new ContentValues();        contentValues.put("stuno","2015");        int id=db.update("Student",contentValues, "stuno=?", new String[]{"6"});//返回值是被影响的行数        textView.append("update id is "+id+"\n");        db.close();    }}

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