Question

我想获得所有记录的数量并获得最后记录：

   $sql_count_sms = "SELECT count(*) as total,content,id FROM android_users_sms WHERE user_id=$id ORDER BY id DESC";
    $result_count_sms = mysql_query($sql_count_sms);
    $row_num_sms = mysql_fetch_assoc($result_count_sms);
    $num_sms     = $row_num_sms['total'];
    $last_my_sms = $row_num_sms['content'];

我可以获得多少条记录，但我无法获得最后content条记录。它返回第一条记录！

我哪里错了？

下面的代码运行正常，但我认为count(*)比mysql_num_rows更快。

    $sql_count_sms = "SELECT content,id FROM android_users_sms WHERE user_id=$id ORDER BY id DESC";
    $result_count_sms = mysql_query($sql_count_sms);
    $row_num_sms = mysql_fetch_assoc($result_count_sms);
    $num_sms     = mysql_num_rows($result_count_sms);
    $last_my_sms = $row_num_sms['content'];

任何解决方案？

Answer 1

你想要的两个结果的粒度是不一样的。如果不使用子查询，则无法将聚合和单行组合到同一结果中。

将谷物视为结果的基本单位。使用GROUP BY和聚合函数可以影响＆＃34; grain＆＃34; ...表上每行一个结果行，或者按user_id等分组...将聚合函数视为a分组的形式。

你可以把它分成两个单独的陈述：

SELECT count(*) as total FROM android_users_sms WHERE user_id = :id;

SELECT * FROM android_users_sms WHERE user_id = :id ORDER BY id DESC LIMIT 1;

此外，根据您的问题，您可能希望将LIMIT 1与ORDER BY结合使用，以获得最后一行。

现在，或许可以直观地反驳，这也应该有效：

SELECT count(*), content, id 
FROM android_users_sms 
WHERE user_id = :id 
GROUP BY id, content 
ORDER BY id 
LIMIT 1;`

这是因为我们改变了＆＃34; grain＆＃34;使用GROUP BY。这是真正的细微差别，我觉得这可能比我现在做的更好。

您也可以使用子查询执行此操作：

SELECT aus.*, 
(SELECT count(*) as total FROM android_users_sms WHERE user_id = :id) AS s1 
FROM android_users_sms AS aus 
WHERE user_id = :id ORDER BY id DESC LIMIT 1;

SQL Order By id和Count star不起作用

1 个答案: