Question

您如何通过输入字符串而不是长ID来删除行？如何编辑我的sql数据库以完成此任务？我想删除不是长id的行，但就像insertRow（String name，int studentNumber，String favoritecolor）一样。所以我可以通过编辑像myDb.deleteRow（String name，int studentNumber，String favoritecolor）来做到这一点???

我的dbAdapter

public class DBAdapter {

    /////////////////////////////////////////////////////////////////////
    //  Constants & Data
    /////////////////////////////////////////////////////////////////////
    // For logging:
    private static final String TAG = "DBAdapter";

    // DB Fields
    public static final String KEY_ROWID = "_id";
    public static final int COL_ROWID = 0;
    /*
     * CHANGE 1:
     */
    // TODO: Setup your fields here:
    public static final String KEY_NAME = "name";
    public static final String KEY_STUDENTNUM = "studentnum";
    public static final String KEY_FAVCOLOUR = "favcolour";

    // TODO: Setup your field numbers here (0 = KEY_ROWID, 1=...)
    public static final int COL_NAME = 1;
    public static final int COL_STUDENTNUM = 2;
    public static final int COL_FAVCOLOUR = 3;


    public static final String[] ALL_KEYS = new String[] {KEY_ROWID, KEY_NAME, KEY_STUDENTNUM, KEY_FAVCOLOUR};

    // DB info: it's name, and the table we are using (just one).
    public static final String DATABASE_NAME = "MyDb";
    public static final String DATABASE_TABLE = "mainTable";
    // Track DB version if a new version of your app changes the format.
    public static final int DATABASE_VERSION = 2;   

    private static final String DATABASE_CREATE_SQL = 
            "create table " + DATABASE_TABLE 
            + " (" + KEY_ROWID + " integer primary key autoincrement, "

            /*
             * CHANGE 2:
             */
            // TODO: Place your fields here!
            // + KEY_{...} + " {type} not null"
            //  - Key is the column name you created above.
            //  - {type} is one of: text, integer, real, blob
            //      (http://www.sqlite.org/datatype3.html)
            //  - "not null" means it is a required field (must be given a value).
            // NOTE: All must be comma separated (end of line!) Last one must have NO comma!!
            + KEY_NAME + " text not null, "
            + KEY_STUDENTNUM + " integer not null, "
            + KEY_FAVCOLOUR + " string not null"

            // Rest  of creation:
            + ");";

    // Context of application who uses us.
    private final Context context;

    private DatabaseHelper myDBHelper;
    private SQLiteDatabase db;

    /////////////////////////////////////////////////////////////////////
    //  Public methods:
    /////////////////////////////////////////////////////////////////////

    public DBAdapter(Context ctx) {
        this.context = ctx;
        myDBHelper = new DatabaseHelper(context);
    }

    // Open the database connection.
    public DBAdapter open() {
        db = myDBHelper.getWritableDatabase();
        return this;
    }

    // Close the database connection.
    public void close() {
        myDBHelper.close();
    }

    // Add a new set of values to the database.
    @SuppressLint("NewApi")
    public long insertRow(String name, int studentNum, String favColour) {

    Cursor c= db.query(true, DATABASE_TABLE, ALL_KEYS, KEY_NAME + "='" + name +"'", null, null, null, null, null, null);

    if(c.getCount()>0){
        return -1;
    }
    c.close();
        /*
         * CHANGE 3:
         */     
        // TODO: Update data in the row with new fields.
        // TODO: Also change the function's arguments to be what you need!
        // Create row's data:
        ContentValues initialValues = new ContentValues();
        initialValues.put(KEY_NAME, name);
        initialValues.put(KEY_STUDENTNUM, studentNum);
        initialValues.put(KEY_FAVCOLOUR, favColour);

        // Insert it into the database.
        return db.insert(DATABASE_TABLE, null, initialValues);
    }

    // Delete a row from the database, by rowId (primary key)
    public boolean deleteRow(long rowId) {
        String where = KEY_ROWID + "=" + rowId;
        return db.delete(DATABASE_TABLE, where, null) != 0;
    }

    public void deleteAll() {
        Cursor c = getAllRows();
        long rowId = c.getColumnIndexOrThrow(KEY_ROWID);
        if (c.moveToFirst()) {
            do {
                deleteRow(c.getLong((int) rowId));              
            } while (c.moveToNext());
        }
        c.close();
    }

    // Return all data in the database.
    @SuppressLint("NewApi")
    public Cursor getAllRows() {
        String where = null;
        Cursor c =  db.query(true, DATABASE_TABLE, ALL_KEYS, 
                            where, null, null, null, KEY_ROWID + " DESC", null, null);
        if (c != null) {
            c.moveToFirst();
        }
        return c;
    }

    // Get a specific row (by rowId)
    public Cursor getRow(long rowId) {
        String where = KEY_ROWID + "=" + rowId;
        Cursor c =  db.query(true, DATABASE_TABLE, ALL_KEYS, 
                        where, null, null, null, null, null);
        if (c != null) {
            c.moveToFirst();
        }
        return c;
    }

    // Change an existing row to be equal to new data.
    public boolean updateRow(long rowId, String name, int studentNum, String favColour) {
        String where = KEY_ROWID + "=" + rowId;

        /*
         * CHANGE 4:
         */
        // TODO: Update data in the row with new fields.
        // TODO: Also change the function's arguments to be what you need!
        // Create row's data:
        ContentValues newValues = new ContentValues();
        newValues.put(KEY_NAME, name);
        newValues.put(KEY_STUDENTNUM, studentNum);
        newValues.put(KEY_FAVCOLOUR, favColour);

        // Insert it into the database.
        return db.update(DATABASE_TABLE, newValues, where, null) != 0;
    }



    /////////////////////////////////////////////////////////////////////
    //  Private Helper Classes:
    /////////////////////////////////////////////////////////////////////

    /**
     * Private class which handles database creation and upgrading.
     * Used to handle low-level database access.
     */
    private static class DatabaseHelper extends SQLiteOpenHelper
    {
        DatabaseHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase _db) {
            _db.execSQL(DATABASE_CREATE_SQL);           
        }

        @Override
        public void onUpgrade(SQLiteDatabase _db, int oldVersion, int newVersion) {
            Log.w(TAG, "Upgrading application's database from version " + oldVersion
                    + " to " + newVersion + ", which will destroy all old data!");

            // Destroy old database:
            _db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);

            // Recreate new database:
            onCreate(_db);
        }
    }
}

和我删除行的代码

myDb.deleteRow(long rowId);

Answer 1

试试这个

//delete a row by string name
    public boolean deleteRow(String name) {
         String where = KEY_NAME + "=?";
            return db.delete(DATABASE_TABLE, where, new String[] { name } ) != 0;

    }

    public void deleteAll() {
        Cursor c = getAllRows();
        long rowId = c.getColumnIndexOrThrow(KEY_ROWID);
        if (c.moveToFirst()) {
            do {
                deleteRow(c.getString((int) rowId));                
            } while (c.moveToNext());
        }
        c.close();
    }

以及您的活动。

myDb.deleteRow("string");

Answer 2

使用 like 关键字，例如。 KEY_STUDENTNUM +“like”+ String，但是列的类型必须是STRING而不是INTEGER，

如何从字符串中删除数据库中的行？

2 个答案: