Question

我的表中有2列table_num，id，名为medium

我希望基于DESC的id序列来回显table_num而不重复。

我正在使用此查询获得结果4,2,7,5,3但我想要的结果是4,5,7,2,3

SELECT DISTINCT table_num FROM medium ORDER BY id DESC

Answer 1

您描述的顺序是升序，而不是降序：

public static String getMacAddr() {
try {
    List<NetworkInterface> all = Collections.list(NetworkInterface.getNetworkInterfaces());
    for (NetworkInterface nif : all) {
        if (!nif.getName().equalsIgnoreCase("wlan0")) continue;

        byte[] macBytes = nif.getHardwareAddress();
        if (macBytes == null) {
            return "";
        }

        StringBuilder res1 = new StringBuilder();
        for (byte b : macBytes) {
            res1.append(String.format("%02X:",b));
        }

        if (res1.length() > 0) {
            res1.deleteCharAt(res1.length() - 1);
        }
        return res1.toString();
    }
} catch (Exception ex) {
}
return "02:00:00:00:00:00";}

Answer 2

执行GROUP BY，按每个table_num的最大ID按降序排序：

select table_num
from medium
group by table_num
order by max(id) desc

要更好地了解其工作原理，请将max(id)添加到选择列表中：

select table_num, max(id) as max_id
from medium
group by table_num
order by max_id desc

按列ID列出列名称顺序，没有重复项

2 个答案: