mysql - 使用 MySQL 选择数据

Question

我在查询中需要解决一个小挑战，我有以下查询:

SELECT SUM(total) AS total, products, DATE_FORMAT(TransDate, '%M') AS month
FROM orders
WHERE Status = 'paid'
AND YEAR(TransDate) = '2016'
GROUP BY Product, YEAR(TransDate), MONTH(TransDate)
ORDER BY TransDate ASC

我对此查询的返回是这样的:

<table border=1>
<tr>
  <th>total</th>
  <th>Product</th>
  <th>Month</th>
</tr>

<tr>
  <td>12000</td>
  <td>Ford Mondeo</td>
  <td>Jan</td>
</tr>
<tr>
  <td>23000</td>
  <td>Camaro</td>
  <td>Jan</td>
</tr>
<tr>
  <td>9000</td>
  <td>Golf</td>
  <td>Jan</td>
</tr>
<tr>
  <td>42000</td>
  <td>Audi A4</td>
  <td>Jan</td>
</tr>


<tr>
  <td>4566</td>
  <td>Ford Mondeo</td>
  <td>Feb</td>
</tr>
<tr>
  <td>35435</td>
  <td>Camaro</td>
  <td>Feb</td>
</tr>
<tr>
  <td>58456</td>
  <td>Golf</td>
  <td>Feb</td>
</tr>
<tr>
  <td>56465</td>
  <td>Audi A4</td>
  <td>Feb</td>
</tr>


<tr>
  <td>3522</td>
  <td>Ford Mondeo</td>
  <td>Mar</td>
</tr>
<tr>
  <td>468132</td>
  <td>Camaro</td>
  <td>Mar</td>
</tr>
<tr>
  <td>25225</td>
  <td>Golf</td>
  <td>Mar</td>
</tr>
<tr>
  <td>54612</td>
  <td>Audi A4</td>
  <td>Mar</td>
</tr>


<tr>
  <td>12000</td>
  <td>Ford Mondeo</td>
  <td>Apr</td>
</tr>
<tr>
  <td>23000</td>
  <td>Camaro</td>
  <td>Apr</td>
</tr>
<tr>
  <td>9000</td>
  <td>Golf</td>
  <td>Apr</td>
</tr>
<tr>
  <td>42000</td>
  <td>Audi A4</td>
  <td>Apr</td>
</tr>
<tr>
  <td>54554</td>
  <td>Beatle</td>
  <td>Apr</td>
</tr>

<tr>
  <td>12000</td>
  <td>Ford Mondeo</td>
  <td>May</td>
</tr>
<tr>
  <td>23000</td>
  <td>Camaro</td>
  <td>May</td>
</tr>
<tr>
  <td>9000</td>
  <td>Golf</td>
  <td>May</td>
</tr>
<tr>
  <td>42000</td>
  <td>Audi A4</td>
  <td>May</td>
</tr>
<tr>
  <td>54554</td>
  <td>Beatle</td>
  <td>May</td>
</tr>
</table>

在我的例子中，披头士汽车只有最近两个月的销售值(value)，而前几个月没有，我想知道是否有任何方法可以让它出现在其他月份，总值(value)为0，并且在汽车实际销售的月份中，其全部值(value)是正确的。

非常感谢您的帮助

Answer 1

使用交叉联接生成所有产品/日期组合。然后使用 left join 引入订单信息。如果您没有其他方便的方法(例如日历表)，您可以使用 orders 上的子查询来获取日期:

SELECT ym.yyyymm, p.product, COALESCE(SUM(o.total), 0) AS total
FROM (SELECT DISTINCT DATE_FORMAT(TransDate, '%M') as yyyymm,
             YEAR(TransDate) as yyyy, MONTH(TransDate) as mm
      FROM orders o
      WHERE TransDate >= '2016-01-01' and TransDate < '2017-01-01'
     ) ym CROSS JOIN
     (SELECT DISTINCT o.product FROM orders o
     ) p LEFT JOIN
     orders o
     ON YEAR(o.TransDate) = ym.yyyy AND
        MONTH(o.TransDate) = ym.mm AND
        o.product = p.product AND
        o.Status = 'paid'
GROUP BY p.Product, ym.yyyymm
ORDER BY MIN(o.TransDate), p.Product;