如何在SQLite列中交换值？

Question

我有表（id，text），我需要在列中交换两个值，如下所示：

Before. 
           1 one. 
           2 two.
           3 three.

After ( 1 and 3 swap)          
           1 three 
           2 two
           3 one

Answer 1

要更新每一行，您需要这样的内容：

void updateMyTableText (MyTableRow row)
{
  ContentValues values = new ContentValues();
  values.put ("text", MyTableRow.text);

  String where = "id = ?";
  String[] whereArgs = new String[1];
  whereArgs[0] = Long.toString (row.id);

  getDb().update ("MyTable", values, where, whereArgs);
}

MyTableRow在哪里

class MyTableRow
{
  long id;
  String text;
}

您还需要一些查询才能获得＆＃34;文字＆＃34;对于第1行和第3行。

以下是进行查询的一种方法：

long getId (String text)
{
  // do the query
  String query = "select id from MyTable where text = ? ";
  String[] args = new String[1];
  args[0] = text;
  Cursor cursor = getDb().rawQuery (query, args);
  if (cursor == null)
    throw new IllegalStateException ("cursor is null");

  try
  {
    // get the results
    if (!cursor.moveToNext())
      return -1; // row not found

    long id = cursor.getLong (0);
    return id;
  }
  finally
  {
    cursor.close();
  }
}

Answer 2

您是否尝试更改行本身的值？大多数数据库系统都不允许您任意交换值，因为假设它们是永久关联的。您可以发出UPDATE命令来永久修改这些值，但暂时执行此操作可能会在返回数据后处理。

UPDATE table_name
SET text=three
WHERE id=1;

UPDATE table_name
SET text=one
WHERE id=3;

Answer 3

// Assuming id1 < id2

void swap(id1,id2)
{
    SQLiteDatabase db = this.getWritableDatabase(); 
        ContentValues CV = new ContentValues();

        // First get the 2 rows
        Cursor res = db.rawQuery("SELECT COLUMN_NAME FROM "+ TABLE_NAME +" WHERE ID IN ("+id1+","+id2+") ORDER BY ID ASC",null);
        res.moveToFirst();
        CV.put("COLUMN_NAME",res.getString(0));
        //Update 1st row with 2nd item
        db.update(TABLE_NAME,CV,"ID = ?",new String[]{id2+""});
        res.moveToNext();
        CV.put("COLUMN_NAME",res.getString(0));
        //Update 2nd row with 1st item
        db.update(TABLE_NAME,CV,"ID = ?",new String[]{id1+""});
}  

希望有帮助！！