如何检查列中是否存在特定数据

Question

我正在开发带有数据库的 java swing 项目。有一个按选项搜索（下拉菜单）来选择用户想要搜索的属性，紧挨着下拉菜单的是一个文本字段，用户可以在其中输入值然后单击搜索。现在我想在该特定列中搜索该特定值（由用户通过 dropdowm 选择）如果它退出我想打印它们“找到”如果不是那么我想显示未找到消息..请找到下面附上图片和代码。

例如：如果用户从下拉列表中选择“客户 ID”，这是一个列名，他们在文本文件中输入 id 作为“123456”，那么如果它在列中退出，那么我需要打印找到的消息，否则我需要找不到打印。

String column = jcombo2.getSelectedItem().toString();
    String value = key.getText();
    DefaultTableModel model = (DefaultTableModel) customerinfo.getModel();
    DefaultTableModel model2 = (DefaultTableModel) customerinfo.getModel();

    try {
     Connection con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost/customerinfo", "root", "");
     Statement st = con.createStatement();
     ResultSet rs;
     String mysqlQuery = "SELECT * FROM `cust_info` WHERE `"+column+"` ='"+value+"'";
     rs =st.executeQuery(mysqlQuery);
     while(rs.next()) {
         String ci = rs.getString("customer id");
         model.addRow(new Object[] {ci});
     }


 }catch(Exception e) {
     System.out.println(e.getMessage());
 }

Answer 1

试试这个：

String mysqlQuery = "SELECT COUNT(*) FROM `cust_info` WHERE `"+column+"` ='"+value+"'";
rs = st.executeQuery(mysqlQuery);
if (rs.next() && (rs.getInt(1) != 0))
  printFoundIt(); // or whatever you want to do
else
  printDidntFindIt(); // or whatever you want to do
st.close();

或者，如果您想用找到的物品填满表格：

String mysqlQuery = "SELECT * FROM `cust_info` WHERE `"+column+"` ='"+value+"'";
rs = st.executeQuery(mysqlQuery);
boolean found_it = false;
while (rs.next())
{
  found_it = true;
  String ci = rs.getString("customer id");
  model.addRow(new Object[] {ci});
}
st.close();

if (found_it)
  printFoundIt(); // or whatever you want to do
else
  printDidntFindIt(); // or whatever you want to do

与之前相同，但在找到第一个元素后直接打印“找到它”：

String mysqlQuery = "SELECT * FROM `cust_info` WHERE `"+column+"` ='"+value+"'";
rs = st.executeQuery(mysqlQuery);
boolean found_it = false;
while (rs.next())
{
  if (!found_it)
  {
    printFoundIt(); // or whatever you want to do
    found_it = true;
  }
  String ci = rs.getString("customer id");
  model.addRow(new Object[] {ci});
}
st.close();

if (!found_it)
  printDidntFindIt(); // or whatever you want to do