22

我有一个简单的安装表:

  • 产品代码
  • 电子邮件
  • 安装槽

如果 install_slot 为 NULL,那么它是一个可用的安装槽。不为空 - 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用安装结果。我想我可以用两个查询来做到这一点,但想知道是否有一种 SQL 方法可以同时完成这一切?

我尝试了以下作为一个疯狂的猜测,但它没有用

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`
4

2 回答 2

50
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只计算NOT NULL值。

于 2012-02-11T23:44:32.630 回答
9

提供的解决方案对我不起作用。我不得不修改如下:

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
于 2016-08-03T16:01:14.977 回答