Question

我正在使用多个关系数据表开发数据收集应用程序。我已经创建了数据库。在第一个表的情况下，代码运行良好。如果我尝试对第二个表运行相同的查询，则即使该表位于数据库中，该表仍显示该表不存在。

数据库结构

public String getName(String Plant) {
    c1 = db.rawQuery("select * from Area where PAd = '" + Plant + "'", new String[]{});
    StringBuffer buffer = new StringBuffer();

    while (c.moveToNext()) {
        String plant = c.getString(0);
        buffer.append("" + plant);
    }

    return buffer.toString();
}

错误日志：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.dbtest, PID: 28350
    android.database.sqlite.SQLiteException: no such table: Area (code 1): , while compiling: select * from Area where PAd = 'Plant02'
        at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
        at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:890)
        at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:501)
        at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
        at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
        at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
        at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:46)
        at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1392)
        at android.database.sqlite.SQLiteDatabase.rawQuery(SQLiteDatabase.java:1331)
        at com.example.dbtest.DatabaseAcess.getName(DatabaseAcess.java:46)
        at com.example.dbtest.MainActivity$3.onClick(MainActivity.java:86)
        at android.view.View.performClick(View.java:6305)
        at android.view.View$PerformClick.run(View.java:24840)
        at android.os.Handler.handleCallback(Handler.java:790)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6501)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

第二张表的表结构

 CREATE TABLE Area (
    Name    TEXT,
    Address TEXT,
    PAd     TEXT
 );

第一个表的表结构

CREATE TABLE Table1 (
   Name    TEXT,
   Address TEXT
);

DatabaseOpenHelper代码。

public class DatabaseOpenHelper extends SQLiteAssetHelper {

    private static final String DATABASE_NAME = "MyExternalDatabase1.db";
    public static final int DATABASE_VERSION = 1;

    public DatabaseOpenHelper(Context context){
        super(context,DATABASE_NAME,null,DATABASE_VERSION);
    }
}

DatabaseAccess代码。

public class DatabaseAcess {

    private SQLiteOpenHelper openHelper;
    private SQLiteDatabase db;
    private static DatabaseAcess instance;
    Cursor c = null;
    Cursor c1 = null;

    private DatabaseAcess(Context context){
        this.openHelper = new DatabaseOpenHelper(context);
    }

    public static DatabaseAcess getInstance(Context context){
        if(instance == null){
            instance = new DatabaseAcess(context);
        }

        return instance;
    }

    public void open(){
        this.db = openHelper.getWritableDatabase();
    }

    public void close(){
        if(db!=null){
            this.db.close();
        }
    }

    public String getAddress(String name){
        c= db.rawQuery("select Address from Table1 where Name = '" + name + "'", new String[]{});
        StringBuffer buffer = new StringBuffer();

        while (c.moveToNext()) {
            String address = c.getString(0);
            buffer.append("" + address);
        }

        return buffer.toString();
    }

    public String getName(String Plant) {
        c1 = db.rawQuery("select Name from Area where PAd = '" + Plant + "'", null);
        StringBuffer buffer = new StringBuffer();

        while (c.moveToNext()) {
            String plant = c.getString(0);
            buffer.append(""+plant);
        }

        return buffer.toString();
    }
}

Answer 1

也许这可以帮助您

public String getName(String Plant) {
Cursor c = db.rawQuery("SELECT * FROM Area WHERE PAd='+Plant+'", null);
    StringBuffer buffer = new StringBuffer();
    while (c.moveToNext()) {
        String plant = c.getString(0);
        buffer.append(""+plant);
    }

    return buffer.toString();
}

Answer 2

我认为外部数据库是指要从asset目录中加载的数据库。在这里，您需要首先将数据库复制到应用程序内部存储中，以使您的代码可以访问该数据库。因此，我建议您在首次运行该应用程序时执行以下操作。

public static final String DB_PATH = "/data/data/" + "com.your.package.name" + "/databases/";

private void copyFromAssetsAndCreateDatabase() {
    InputStream yourDatabaseFromAsset;

    try {
        yourDatabaseFromAsset = getApplicationContext().getAssets().open("MyExternalDatabase1");

        File dir = new File(DataHelper.DB_PATH);
        if (!dir.exists()) dir.mkdir();
        File f = new File(DataHelper.DB_PATH + "MyExternalDatabase1" + ".sqlite");
        if (!f.exists()) {
            f.createNewFile();
        }

        OutputStream mOutput = new FileOutputStream(f);
        byte[] mBuffer = new byte[1024];
        int mLength;

        while ((mLength = yourDatabaseFromAsset.read(mBuffer)) > 0)
            mOutput.write(mBuffer, 0, mLength);

        mOutput.flush();
        mOutput.close();
        mInputEnglish.close();

    } catch (Exception e) {
        e.printStackTrace();
    }
}

现在，当将数据库从外部文件夹复制到数据库通常位于的内部存储中时，它应该可以找到数据库而没有任何错误。我不知道第一个数据库。我认为它是在您的应用程序中使用CREATE TABLE语句创建的。

希望有帮助。

Answer 3

一个可能的原因是您第一次只创建了第一个表。之后，为第二个表追加代码。注意数据库已创建，将不会再次调用onCreate（）。您应该升级数据库版本并在onUpgrade（）中创建第二个表。

我以前犯过同样的错误。

Android外部数据库中的SQLite SELECT查询-表错误

3 个答案: