如何通过选择语句合并 2 个组答案

【问题标题】：How to merge 2 group by select statements如何通过选择语句合并 2 个组
【发布时间】：2020-07-21 03:19:00
【问题描述】：

我有 2 个表格，1 个用于免费用户，1 个用于付费用户，它们都在跟踪点击，我需要为每个附属链接显示谁是引荐来源（域），用户有时可能是免费用户并且有时可能是付费用户，因此我需要合并两个表中的两个统计信息。

这个查询不起作用：

SELECT ref,COUNT(ref) AS clicks 
FROM click_analytics_free 
WHERE link_id = '$link_id'
GROUP BY ref 
UNION ALL
SELECT ref,COUNT(ref) AS clicks 
FROM click_analytics_paid 
WHERE link_id = '$link_id '
GROUP BY ref

【问题讨论】：

标记您正在使用的 DBMS。

标签： sql merge group-by union

【解决方案1】：

你可以做聚合：

SELECT ref, 
       SUM(CASE WHEN flag = 'free' THEN 1 ELSE 0 END) AS free_click,
       SUM(CASE WHEN flag = 'paid' THEN 1 ELSE 0 END) AS paid_click
FROM (SELECT ref, 'free' as flag 
      FROM click_analytics_free 
      WHERE link_id = '$link_id '
      UNION ALL
      SELECT ref, 'paid' as flag 
      FROM click_analytics_paid 
      WHERE link_id = '$link_id'
     ) t
GROUP BY ref;

【讨论】：

【解决方案2】：

你可以做一个union all 然后再次聚合：

SELECT ref, SUM(free_clicks), SUM(paid_clicks), 
       SUM(free_clicks + paid_clicks)
FROM ((SELECT ref, COUNT(ref) AS free_clicks, 0 as paid_clicks
       FROM click_analytics_free
       WHERE link_id = ?
       GROUP BY ref
      ) UNION ALL
      (SELECT ref, 0, COUNT(ref) AS paid_clicks
       FROM click_analytics_paid
       WHERE link_id = ?
       GROUP BY ref
      )
     ) c
GROUP BY ref;

? 是一个参数占位符。您的代码应该使用参数而不是修改查询字符串。

【讨论】：