mysql - 在 select 语句中计算 where 和 if

Question

您好，我正在尝试在 mysql 中编写堆积条形图，首先我需要正确查询，并需要一些帮助。

目前我有:

SELECT
COUNT(TargetDate) AS Planned,
COUNT(StartDate) AS Completed,
MONTHNAME(TargetDate) AS `Month`,
StartDate,
AssessmentStatus
FROM AuditCycleAssessments
WHERE (Year(TargetDate) = Year(now()))
GROUP BY MONTHNAME(TargetDate)
ORDER BY Month(TargetDate)

效果很好，看起来像 screenshot

但是我需要更改第 3 行以包含它自己的 where 语句，例如...

  (COUNT(StartDate) if AssessmentStatus=3) AS Completed,

第 1 点，有人可以帮我实现这个目标吗。

谢谢

Answer 1

使用 CASE 语句执行条件 COUNT

SELECT
    COUNT(TargetDate) AS Planned,
    COUNT(CASE WHEN AssessmentStatus=3 THEN StartDate END) AS Completed,
    MONTHNAME(TargetDate) AS `Month`,
    StartDate,
    AssessmentStatus
FROM AuditCycleAssessments
WHERE (Year(TargetDate) = Year(now()))
GROUP BY MONTHNAME(TargetDate)
ORDER BY Month(TargetDate)