Question

我试图在Android应用中实现递归功能;

首先，我尝试了（递归功能）来自＆＃39; cmd＆＃39;窗口：

我创建了一个表：

 CREATE TABLE tree(
 id_tree integer PRIMARY KEY AUTOINCREMENT,
 id_boss TEXT,
 id_child TEXT,
 answ TEXT);

然后插入一些值：

 INSERT INTO tree(id_boss,id_child,answ) VALUES('1','2','T');
 INSERT INTO tree(id_boss,id_child,answ) VALUES('1','3','F');
 INSERT INTO tree(id_boss,id_child,answ) VALUES('2','P1','T');
 INSERT INTO tree(id_boss,id_child,answ) VALUES('2','4','F');
 INSERT INTO tree(id_boss,id_child,answ) VALUES('3','P2','T');
 INSERT INTO tree(id_boss,id_child,answ) VALUES('3','8','F');

然后我运行一个现在可用于sqlite 3.8的递归查询：

 WITH RECURSIVE
 under_alice(name,level) AS (
   VALUES('1','0')
   UNION ALL
   SELECT tree.id_child, under_alice.level+1
     FROM tree, under_alice
    WHERE tree.id_boss=under_alice.name 
    ORDER BY 2 DESC
    )
   SELECT  substr('..........',1,level*3) || name FROM under_alice;

结果运行正常：

  1
  ...2
  ......4
  ......P1
  ...3
  ......8
  ......P2

然后我选择id_child，其中id_boss =＆＃39; 1＆＃39;并回答=＆＃39; T＆＃39;使用此查询;

  WITH RECURSIVE 
  under_alice(name,level) AS ( 
  VALUES('1','0') 
  UNION ALL 
  SELECT tree.id_child, under_alice.level+1 FROM tree, under_alice WHERE 
  tree.id_boss=under_alice.name and answ = 'T' and tree.id_boss='1' 
  ORDER BY 2 DESC
  )
  SELECT  substr('..........',1,level*3) || name FROM under_alice;

这个结果运行良好：

 1
 ...2

这一切都可以在cmd提示符下运行，但是当我尝试在我的Android应用程序中实现它时，我会遇到一些错误（例如，无法执行）：

这是我从Android应用程序执行查询的代码：

 try {
 SQLiteDatabase db = dbHandler.getWritableDatabase();
      String q = "WITH RECURSIVE 
      under_alice(name,level) 
      AS ( VALUES('1','0') 
      UNION ALL 
      SELECT tree.id_child, under_alice.level+1 FROM tree, under_alice 
      WHERE tree.id_boss=under_alice.name and answ = 'T' and tree.id_boss='1'         ORDER BY 2 DESC)
      SELECT  max(name) as au FROM under_alice;";     
      Cursor eq = db.rawQuery(q, null);
      eq.moveToFirst();
      int au = eq.getColumnIndex("au"); 
      String sau = eq.getString(au);
      makeToast(""+sau); // if execute succes, create a toast message

        } catch (Exception e) {
    // TODO: handle exception
    makeToast("failed query"); // if query filed
    }
    }

如何使这项工作？我的查询有什么问题吗？

如何在Android设备上实现sqlite3的递归功能

0 个答案: