在单个查询中使用多个计数

Question

我在下面有一个查询，我想返回一天的严重警报和警告警报的总数，但是我遇到的问题是，当我在几天内执行此操作时，它会添加指定日期的严重警报

SELECT alertDate as "Alert Date",
    (SELECT COUNT(alertType) FROM alerts WHERE alertDate BETWEEN '2016/02/15' AND '2016/02/16' AND UPPER(alertType)='CRITICAL') as Critical,
    (SELECT COUNT(alertType) FROM alerts WHERE alertDate BETWEEN '2016/02/15' AND '2016/02/16' AND UPPER(alertType)='WARNING') as Warning
FROM alerts
where alertDate BETWEEN '2016/02/15' AND '2016/02/16'
GROUP BY alertDate;

尝试了上面的代码，但显然我无法在子查询中添加“ group by”子句，我认为这是问题所在，请提供有关如何进行此操作的任何帮助...

Answer 1

您可以为此使用sum（case）：

SELECT alertDate as "Alert Date",
    sum(case when UPPER(alertType)='CRITICAL' then 1 end) as Critical,
    sum(case when UPPER(alertType)='WARNING' then 1 end) as Warning
FROM alerts
where alertDate BETWEEN '2016/02/15' AND '2016/02/16'
GROUP BY alertDate;

Answer 2

您需要条件聚合- case在聚合函数中。 我可以这样写：

SELECT alertDate as AlertDate,
       SUM(CASE WHEN UPPER(alertType) = 'CRITICAL' THEN 1 ELSE 0 END) as Critical,
       SUM(CASE WHEN UPPER(alertType) = 'WARNING' THEN 1 ELSE 0 END) as WARNING
FROM alerts a
WHERE alertDate BETWEEN '2016-02-15' AND '2016-02-16'
GROUP BY alertDate;

如果您使用的是MySQL，则可以将其简称为：

SELECT alertDate as AlertDate,
       SUM(UPPER(alertType) = 'CRITICAL') as Critical,
       SUM(UPPER(alertType) = 'WARNING') as Warning
FROM alerts a
WHERE alertDate BETWEEN '2016-02-15' AND '2016-02-16'
GROUP BY alertDate;

注意其他一些变化：

• 不需要子选择。
• 我从AlertDate删除了空间。 我只是不喜欢需要转义的列别名。
• 我取代了/有-中日文字-连字符是ISO 8601兼容。

Answer 3

您可能应该使用条件计数，例如

SUM( case when alertDate BETWEEN '2016/02/15' AND '2016/02/16' 
     AND UPPER(alertType)='CRITICAL' then 1 else 0 end) as Critical,