Question

我为我的班级做了一个名为亚马逊的项目数据库。在本报告中，我想从最好的selled产品到最后一个selled显示。我希望得到最顶级的产品，并展示购买它们的所有客户并显示和他们的电子邮件以及他们推出的该产品的数量。好的，我可以完全展示最好的selled产品。我知道如何获得第一行（如果两个或更多产品具有相同的销售数量，我会遇到问题）但我不能从结果集中的第一个表中获取标题其他查询：/ 谁能帮我解决这个问题？

void report2 (Connection conn) 
        throws SQLException, IOException {

String query0 = "select title, SUM (quantityb) AS total from product,buy where id = idb group by title order by total DESC";


String title,title2,name,email,t;
int quan,quanp;

Statement stmt = conn.createStatement (); 
ResultSet rset0;

System.out.print("\n\n************************************MOST POPULAR PRODUCTS************************************\n");

System.out.print("         TITLE OF THE PRODUCT                                                TOTAL PURCHASED\n"+
         "--------------------------------------------                            -------------------------\n");



try {
rset0 = stmt.executeQuery(query0);
   } catch (SQLException e) {
    System.out.println("Problem reading purchases");
    while (e != null) {
    System.out.println("Message     : " + e.getMessage());
    e = e.getNextException();
    }
    return;
}
while (rset0.next())
{

    title = rset0.getString(1);
    quan = rset0.getInt(2);


    System.out.printf("%-108s   %-3d \n ",title,quan);
}



PreparedStatement statement = conn.prepareStatement(query0);
statement.setMaxRows(1);
ResultSet rset1 = statement.executeQuery();
while (rset0.next())
{

  title2= rset1.getString(1);

}


   String query2 = "select  
   String query1 = "Select fname,email,quantityb"+
                  "from custumer,product,buy"+
                  "where email = emailb"+
                  "and id = idb"+
                  "and title ='"+title2+"'";



System.out.print("..............................Who Purchased the most popular product.............................\n");

System.out.print("PRODUCT:"+title2+"\n\n");
System.out.print("     FIRST NAME                      EMAIL                 QUANTITY\n"+
         "---------------------    -----------------------------  ------------------\n");

ResultSet rset2;

try {
rset2= stmt.executeQuery(query1);

} catch (SQLException e) {
    System.out.println("Problem reading people");
    while (e != null) {
    System.out.println("Message     : " + e.getMessage());
    e = e.getNextException();
    }
    return;
}

while (rset2.next())
{

   name=rset2.getString(1);
   email=rset2.getString(2);
   quanp=rset2.getInt(3);


    System.out.printf("%-8s \t\t\t%-25s\t\t\t %3d \n ",name,email,quanp);
}




stmt.close();
}

RESULT

commerce.java:405：变量title2可能尚未初始化 “and title ='”+ title2 +“'”; ^ 1错误

Answer 1

这似乎是一项功课或练习。

variable title2 might not have been initialized

是因为您尚未初始化任何字符串变量，包括title2

更改

String title,title2,name,email,t;致

String title="", title2="", name="", email="", t="";。

第二，

String query2 = "select

这是不完整的，它应该是带有结尾引号和分号的有意义的值。

赞String query2 = "select * from tblName";

在附注中，
始终提供问题的完整错误堆栈。

从结果集中获取信息

1 个答案: