这段代码是什么意思，friends表是怎么设计的

[forTribeforXuanmo]

String sql = "SELECT * FROM friends WHERE username = ?"; try { pstmt = conn.prepareStatement(sql); pstmt.setString(1, username); resultSet = pstmt.executeQuery(); if (resultSet.next()) { for (int i = 1; i <= 20; i++) { if (resultSet.getString("friend_" + i) == null) { return "friend_" + i; } } }
字段的数量不算固定的吗，不算就两个字段，一个Username 一个friend