Question

我正在尝试计算两个位置之间的距离。一个位置的lat long现在是硬编码的（我稍后会通过考虑gps中的值来改变它），其他位置存储在数据库中。我使用以下查询

Cursor c = sampleDB.rawQuery("SELECT NAME, CONTACT,((LAT -" +
        " LATCUR) * (LAT - LATCUR) + ((LONG - LONGCUR) * 2) * ((LONG - LONGCUR) * 2)) " +
        "AS DISTANCE FROM AMBULANCE ORDER BY DISTANCE", null );

其中LATCUR和LONGCUR是当前值。我收到错误，因为没有名为latcur的列。我该怎么办？

我将latcur和longcur值声明为 public static double LATCUR = 39.991932; public static double LONGCUR = -83.012352;

代码：公共类MainActivity扩展了ListActivity {

private final String DBNAME = "SERVICES";
private final String TABLENAME = "AMBULANCE";
public static double LATCUR = 39.991932;
public static double LONGCUR = -83.012352;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);


    ArrayList<String> results = new ArrayList<String>();
    SQLiteDatabase sampleDB = null;

    try {

        sampleDB =  this.openOrCreateDatabase(DBNAME, MODE_PRIVATE, null);

        sampleDB.execSQL("CREATE TABLE IF NOT EXISTS " +
                TABLENAME +
                " (NAME VARCHAR, CONTACT VARCHAR," +
                " LAT float, LONG float, LATC double, LONGC double);");

Cursor c = sampleDB.rawQuery（“SELECT NAME，CONTACT，（（LAT - ”+ “LATCUR）*（LAT - LATCUR）+（（LONG - LONGCUR）* 2）*（（LONG - LONGCUR）* 2））”+ “按距离划分的救援距离”，无效）;

        if (c != null ) {
            if  (c.moveToFirst()) {
                do {
                    String NAME = c.getString(c.getColumnIndex("NAME"));
                    String CONTACT = c.getString(c.getColumnIndex("CONTACT"));
                    results.add("" + NAME + ",CONTACT: " + CONTACT);
                }while (c.moveToNext());
            } 
        }

        this.setListAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,results));


    }

Answer 1

你引用了它们。您需要在引用的SQL字符串之外进行所有数学运算。

Answer 2

试试这个......

    Cursor c = sampleDB.rawQuery("SELECT NAME, CONTACT,((LAT -"+LATCUR+") * (LAT - "+LATCUR+") + ((LONG - "+LONGCUR+") * 2) * ((LONG - "+LONGCUR+") * 2)) " +
 "AS DISTANCE FROM AMBULANCE ORDER BY DISTANCE", null );

希望它有所帮助。

android-sqlite-使用lat long值在两点之间的距离

2 个答案: