Question

我有一个简单的安装：

表

prod_code
电子邮件
install_slot

如果install_slot为NULL，那么它是一个可用的安装槽。不为null - 然后，使用插槽。我需要返回给定产品和电子邮件的总安装结果，以及给定产品和电子邮件的已安装结果。我想我可以通过两个查询来做到这一点，但是想知道是否有一种SQL方法可以在一个中完成这一切？

我尝试了下面的猜测，但无效。

SELECT
    i1.`prod_code`,
    COUNT(i1.`email`) AS total_installs,
    COUNT(ISNULL(i2.`install_slot`)) AS used_installs
FROM
    `installs` AS i1
JOIN
    `installs` AS i2
ON
    i1.`prod_code` = i2.`prod_code`
WHERE
    i1.`email` = 'example@example.com'
GROUP BY
    i1.`prod_code`,i2.`prod_code`

Answer 1

SELECT prod_code,
       COUNT(email) AS total_installs,
       COUNT(install_slot) AS used_installs
FROM installs
WHERE email='example@example.com'
GROUP BY prod_code

COUNT仅计算NOT NULL个值。

Answer 2

提供的解决方案对我不起作用。我必须修改如下：

SELECT prod_code,
       COUNT(NULLIF(email,'')) AS total_installs,
       COUNT(NULLIF(install_slot,'')) AS used_installs
FROM installs
WHERE email='example@example.com'
GROUP BY prod_code

MySQL - 如何计算空值而不是空值？

2 个答案: