如何从两个表中获取最新的5个公司数据

Question

我在mysql数据库中有2个表。

a）公司

cid    company_name  
===================
1      AstraZeneca
2      Emirates
3      Development Bank of Singapore
4      Royal Copenhagen
5      xxx  
6      xxx  

2）历史

hid   user_id   view_id  is_save  mark_as  view date
==============================================================
1     2         2        0        3        2016-08-25 22:06:12
2     3         3        1        3        2016-08-25 22:07:12
3     3         3        0        1        2016-08-25 22:08:12
4     3         2        0        1        2016-08-25 22:09:12
5     2         4        0        1        2016-08-25 22:10:12
6     4         5        0        1        2016-08-25 22:11:12
7     4         6        0        1        2016-08-25 22:12:12

此view_id包含cid值。

现在，我始终希望根据company_name表company将history表中的最新5 view_id显示为升序。

为此，我正在进行以下查询。但company_name未显示ASC或DESC订单

以下是查询：

$getViewID3 = mysqli_query($link, "SELECT view_id, hid, is_save FROM history WHERE user_id = '$user_id' AND mark_as = 3 GROUP BY view_id ORDER BY view_date DESC LIMIT 5 ");  

if(mysqli_num_rows($getViewID3) > 0 ) { 

   while( $fetchViewId3 = mysqli_fetch_array($getViewID3) ) {
   $viewid3 = (int) $fetchViewId3['view_id'];
   $hid3 = (int) $fetchViewId3['hid'];
   $is_save3 = (int) $fetchViewId3['is_save'];

   $getCompany = mysqli_query($link, "SELECT company_name FROM company WHERE cid = '$viewid3' ORDER BY company_name DESC");

   if(mysqli_num_rows($getCompany) > 0 ) {

      while ($fetchCompany2  = mysqli_fetch_array($getCompany)) {
         $cName = htmlspecialchars($fetchCompany2['company_name']);
         $url_link = "{$url}company.php?cid=$viewid";

         if($is_save3 == 1) {
            $checked = 'checked = "checked"';
         } else {
            $checked = '';
         }

         echo "<li><a onClick='window.document.location=\"$url_link\"'>&nbsp;&nbsp;$cName </a> <input type='checkbox' class='data_save' $checked data-hid='$hid' data-saveid='$viewid3' name='save_history'></li>";
      }   
   }
}

例如：结果显示：A，E，D，R，L字母顺序。 它应显示：A，D，E，L，R字母从company_name列开始排序。

Answer 1

如果我没有误解：

SELECT 
C.company_name
FROM company C 
INNER JOIN 
(
    SELECT 
    view_id,
    MAX(view_date) max_view_date
    FROM history 
    WHERE is_save IN (0,1) AND mark_as = 3
    GROUP BY view_id
    ORDER BY max_view_date DESC 
    LIMIT 5
) AS t
ON C.cid = t.view_id
ORDER BY C.company_name ASC;

注意：

由于您需要最新的5家公司，以下查询会将最后view_date放在view_id旁边。

现在，如果您根据max_view_date的降序顺序对这些行进行排序，然后将结果限制为5，那么您最多可获得五个view_id个从内部查询。

稍后，此结果集与公司表之间的简单INNER JOIN将完成该作业。

抱歉，按照公司名称的升序排序最终结果将完成工作。

修改

为了从history表中获取company_name表和company列的所有列：

SELECT 
C.company_name,
t.*
FROM company C 
INNER JOIN
(
    SELECT 
    history.*
    FROM history
    INNER JOIN 
    (
        SELECT 
        view_id,
        MAX(view_date) max_view_date
        FROM history 
        WHERE is_save IN (0,1) AND mark_as = 3
        GROUP BY view_id
        ORDER BY max_view_date DESC 
        LIMIT 5
    ) AS latestHistory
    ON history.view_id = latestHistory.view_id AND history.view_date = latestHistory.max_view_date
) AS t
ON C.cid = t.view_id
ORDER BY C.company_name ASC;