Question

我使用一个非常简单的删除查询“DELETE FROM S WHERE SNO =”+ row;

虽然在运行时我得到错误但是在输入我想要删除S1时没有列S1存在？

我100％确定我在数据库中有S1。

错误：

java.sql.SQLException：[SQLITE_ERROR] SQL错误或缺少数据库（没有这样的列：S1）

我的删除方法：

public void Delete() throws SQLException, ClassNotFoundException {
    String query = "";
    //asks the user for a tablename.
 String tablename = JOptionPane.showInputDialog("Which table do you want to delete from?");
 String row = JOptionPane.showInputDialog("Which row do you want to delete?");

 // checks if the input is equal to any of these names and changes the query thereafter.
        switch (tablename) {
            case "S":
                query = "DELETE FROM S WHERE SNO="+row;
                break;
            case "J":
                query = "DELETE FROM J WHERE JNO ="+row;
                break;
            case "P":
                query = "DELETE FROM P WHERE PNO ="+row;
                break;
            case "SPJ":
                query = "DELETE FROM SPJ WHERE SNO ="+row;
                break;
                 case "s":
                query = "DELETE FROM S WHERE SNO ="+row;
                break;
            case "j":
                query = "DELETE FROM J WHERE JNO ="+row;
                break;
            case "p":
                query = "DELETE FROM P WHERE PNO ="+row;
                break;
            case "spj":
                query = "DELETE FROM SPJ WHERE SNO ="+row;
                break;
        }
Connection c = null;
Statement stmt = null;
try {
  Class.forName("org.sqlite.JDBC");
  c = DriverManager.getConnection("jdbc:sqlite:test.db");
  c.setAutoCommit(false);
  System.out.println("Opened database successfully");

  stmt = c.createStatement();
  ResultSet rs = stmt.executeQuery(query);

  rs.close();
  stmt.close();
  c.close();

} catch ( Exception e ) {
  System.err.println( e.getClass().getName() + ": " + e.getMessage() );

}
System.out.println("You have deleted from " + tablename + " where rowID = " + row);
}

Answer 1

在SQL中，字符串用引号分隔：

query = "DELETE FROM x WHERE xNO = '" + row + "'";

如果没有引号，单词将被解释为表名或列名。

无论如何，为避免格式化问题（当字符串包含引号时）并避免SQL注入攻击，最好使用参数：

query = "DELETE FROM x WHERE xNO = ?";
...
PreparedStatement ps = c.prepareStatement(query);
ps.setString(1, row);
rs = ps.executeQuery();

Sqlite删除错误

1 个答案: