Java SQL 查询结果集总是返回 null 找不到解决办法

Question

I am trying to check if a user entered Username and password matches one in my data base however what ever I try the result set still comes up null. the sql varible is set to the username and the pass is set to the password however when ever i enter the correct details it shows up with no results

public boolean Login(){
    boolean valid = true;
        try {
            String stmt = "SELECT * From TBLUser where User = ? and Password = ? ;";
            PreparedStatement pstmt = conn.prepareStatement(stmt);
            pstmt.setString(1, sql); pstmt.setString(2, pass);
            ResultSet rs = pstmt.executeQuery();
            if(!rs.next()){
                valid = false;
            }
        } catch (SQLException e) {
            System.err.println("Error: "+e);
        }
    return valid;
}

Answer 1

Also, better practice:

public boolean Login(String asql, String apass){
    boolean valid = true;
    PreparedStatement pstmt = null;
    ResultSet rs = null;

        try {
            String stmt = "SELECT * From TBLUser where User = ? and Password = ? ";
            pstmt = conn.prepareStatement(stmt);
            pstmt.setString(1, asql); 
            pstmt.setString(2, apass);

            rs = pstmt.executeQuery();

            valid = (!rs.next());

        } catch (SQLException e) {
            e.printStaceTrace();
        } finally { // cleanup
          try { rs.close(); } catch (Exception ex) {}
          try { ps.close(); } catch (Exception ex) {}
        }
    return valid;
}

Answer 2

The problem with the application is not the code but the database as User one of the column names is a reserved word so this change fixed the problem thanks to @Grayson for all the help

public boolean Login(){
boolean valid = true;
    try {
        String stmt = "SELECT * From TBLUser where UserName = ? and Password = ? ;";
        PreparedStatement pstmt = conn.prepareStatement(stmt);
        pstmt.setString(1, sql); pstmt.setString(2, pass);
        ResultSet rs = pstmt.executeQuery();
        if(!rs.next()){
            valid = false;
        }
    } catch (SQLException e) {
        System.err.println("Error: "+e);
    }
return valid;

}

Answer 3

Use unit cap with " " to save your column-Table like

Create Table "TBLUser"{ "User" char... "Password"... }

similarly, your select query will change String stmt = "SELECT * From \\"TBLUser\\" where \\"User\\" = ? and \\"Password\\" = ? "

This should work.