php - 获取一年中每个月的总计，包括没有结果的月份

Question

我想回显每月创建的发票总数。

下面的代码到目前为止有效，但如果一个月内没有结果，我需要 0。

$sql = "SELECT MONTH( invoice_date ) AS MONTH, SUM(`invoice`.`total`) as total
    FROM `invoices`
    WHERE YEAR(invoice_date) = '2019'
    GROUP BY MONTH(invoice_date)";
$result = mysqli_query($con,$sql);
while($data = mysqli_fetch_array($result))
{
    $total = $data['total'];
    $month = $data['month'];
}

我想要的是这样的:

Jan 500
Feb 300
Mar 0
Apr 500
etc...

我得到的是这个

一月 500二月 300四月 500

...因为我的数据库中没有包含 Mar 的条目。

如果我每个月循环执行查询，它工作正常，但我知道我不应该以这种方式使用它，并且有更好的方法!？

Answer 1

使用 UNION ALL 创建一个查询，返回所有月份数字 1-12 和 LEFT JOIN 到您的查询:

SELECT m.MONTH, COALESCE(t.total, 0)
FROM (
  SELECT 1 AS MONTH UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL 
  SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL
  SELECT 9 UNION ALL SELECT 10 UNION ALL SELECT 11 UNION ALL SELECT 12
) AS m LEFT JOIN (
  SELECT MONTH( invoice_date ) AS MONTH, SUM(`invoice`.`total`) as total
  FROM `invoices`
  WHERE YEAR(invoice_date) = '2019'
  GROUP BY MONTH(invoice_date)
) AS t ON t.MONTH = m.MONTH