Question

使用以下查询，我从db中的两个表中获取数据。但是如果COL5为空，则不显示（TABLE1）的数据。它还应该显示其他数据？

SQLiteDatabase db = mHelper.getReadableDatabase();
final List<Dettaglio1> dettagli1 = new ArrayList<Dettaglio1>();     

String sql = "SELECT C._id, " +
            "B.col1, " +
            "B.col2, " +
            "B.col3, " +
            "B.col4, " +
            "B.col5, " +
            "B.col6, " +
            "SUM(C.col01), " +
            "C.col02, " +
            "C.col03 " +
            "FROM table1 B LEFT JOIN table2 C ON (B.col5 = C.col02)";

Cursor cur = db.rawQuery(tabella_conti, null); 
  while (cur.moveToNext()){
      Dettaglio1 d01 = new Dettaglio1();
        d01.id= cur.getString(0);   
        d01.col1= cur.getString(1);                     
        d01.col2= cur.getDouble(2);         
        d01.col3= cur.getString(3);             
        d01.col4 = cur.getString(4);                            
        d01.col5= cur.getString(5);                 
        d01.col6 = cur.getString(6);
        d01.col01 = cur.getDouble(7);                   
        d01.col02 = cur.getString(8);               
        d01.col03= cur.getString(9);                
        dettagli1.add(d01);     

        }
        cur.close();        
        db.close();

....
....
}

Answer 1

如果要包含NULL值，则应使用LEFT或RIGHT连接，如下所示：

... from table1 as B RIGHT JOIN table2 as C ON (B.col5 = C.col02)

如果某些平台不支持RIGHT join（感谢@ user3608814，请参阅注释）使用LEFT join并更改表的顺序：

... from table2 as C LEFT JOIN table1 as B ON (C.col02 = B.col5)

更新
如果这没有帮助（当您写完时table2中没有数据，但仍需要结果），您应重新组织< / strong>您的数据方案：
向table2添加明确的外键，将其链接到table1。设为table2.extID列。然后可以像这样查询：

... from table1 as B LEFT JOIN table2 as C ON (B._ID = C.extID)

Android SQLite null选择

1 个答案: