<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<Button
    android:id="@+id/creat"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Create database"/>
<Button
    android:id="@+id/add"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Add data"/>
<Button
    android:id="@+id/updata"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Updata data"/>
<Button
    android:id="@+id/deletedata"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Delete data"/>

</LinearLayout>

 private void queryStudents() {

        // 相当于 select * from students 语句
        Cursor cursor = mSQLiteDatabase.query(SQLiteDbHelper.TABLE_STUDENT, null,
                "cls_id > ? and id >= 1", new String[]{"3"},
                null, null, null, null);

        // 不断移动光标获取值
        while (cursor.moveToNext()) {
            // 直接通过索引获取字段值
            int stuId = cursor.getInt(0);

            // 先获取 name 的索引值，然后再通过索引获取字段值
            String stuName = cursor.getString(cursor.getColumnIndex("name"));
            Log.e("", "id: " + stuId + " name: " + stuName);
        }
        // 关闭光标
        cursor.close();
    }