Question

我有两张桌子..类别＆amp;交易。最终，我想做以下事情：

// foreach category
    // Display category title
    // show 3 entries in deals where it matches category title above, along with a link saying: "View (count) More Deals

现在，我有几种方法可以做到这一点：

// The "bad" way:
// foreach category
    // fetch count of total deals in this category
    // Display category title (once) 
        // Fetch & Display 3 deals
    // Display "View (count) more deals
// This is just quite a few queries for one page

“其他”方式：

    SELECT count(deals.id),
           category.name as category_name,
           deal.name as deal_name
      FROM $db[ddd_deals] as deals
      JOIN $db[ddd_categories] 
        ON $db[ddd_categories].id = $db[ddd_deals].category_id
     WHERE deals.city_id = '$_SESSION[city_id]'
  ORDER BY $db[ddd_categories].name

除了显示每个类别中的交易数量之外，上述所有内容都会执行，并且每个类别仅显示3笔交易

- 我应该从交易表中选择（或从类别表中选择，然后获取交易？）

// I also tried the following. It returns what category and deal, but the count is off (it is only displaying 1):

  SELECT count(deals.id) as cc, 
         cat.name as cat_name, 
         deals.name as name 
    FROM ddd_categories as cat
    JOIN ddd_deals as deals 
      ON deals.category_id=cat.id
GROUP BY deals.id
ORDER BY cat.id

Answer 1

您需要GROUP BY cat.id而不是deals.id。尝试以下：

SELECT count(deals.id) as cc, cat.name as cat_name, deals.name as name
FROM ddd_categories as cat JOIN ddd_deals as deals ON deals.category_id=cat.id
GROUP BY cat.id

Answer 2

只是一个快速的，无论你是通过deals.id或..分组，订单来自不正确的地方。

select cc, cat_name, name from (
   SELECT count(deals.id) as cc, cat.name as cat_name, deals.name as name 
   FROM ddd_categories as cat
   JOIN ddd_deals as deals on deals.category_id=cat.id
   GROUP BY deals.id
)
ORDER BY xxx;

Mysql - 带有计数项的子查询

2 个答案: