mysql - MYSQL SELECT 语句中如何划分子查询？

Question

我试图在 select 语句中划分 2 个子查询，如何做到这一点？ 预期结果:

total_completed/总计 = 率。

SELECT (SELECT Count(id)
    FROM   campaign_results)                  AS total,
   (SELECT Count(id)
    FROM   campaign_results
    WHERE  status = 'completed') AS total_completed,
   ( total_completed / total )                AS rate
FROM   `campaigns`  

Answer 1

您可以在此处使用条件聚合并避免将子查询放入 select 子句中:

SELECT
    COUNT(*) AS total,
    COUNT(CASE WHEN status = 'completed' THEN 1 END) AS total_completed,
    COUNT(CASE WHEN status = 'completed' THEN 1 END) / COUNT(*) AS rate
FROM campaigns;