如何使用netbeans使用數據庫語句進行計數

Question

我在計算輸入並將其與數據庫中的數據字段進行匹配，然後計算狀態並顯示輸入已借入的書籍數量。

 Statement statement = conn.createStatement(); 

     String sql = "SELECT COUNT(jtfMemberID.getText()) as num FROM LOAN WHERE LOAN_STATUS='BORROWED'"; 

     ResultSet rs1 = statement.executeQuery(sql); 
     int personCount = 0; 

     if(rs1.next()) { 
      personCount = rs1.getInt("num"); 
      jlbBookBorrow.setText(rs1.getString(personCount)); 
     }else{ 
      jlbBookBorrow.setText("0"); 
     } 

Answer 1

文本jtfMemberID.getText()將字面上你SQLString解釋。你需要提取出來：

String sql = "SELECT COUNT(" + jtfMemberID.getText() + ") as num FROM LOAN WHERE LOAN_STATUS='BORROWED'"; 

此外，爲了防止SQL Injection攻擊，可以考慮使用PreparedStatement。