[英]Slow MYSQL query using COUNT and LEFT JOIN
我正在使用以下查詢COUNT記錄並在MySQL中顯示記錄。 雖然它可以正常顯示並正常工作,但速度非常慢。 我認為部分原因是因為HTG_ScheduleRequest表非常大。 有沒有更好的方法來安排此查詢以加快速度?
SELECT HTG_TechProps.EmpNumber,
HTG_TechProps.EmpFirstName,
HTG_TechProps.EmpLastName,
HTG_TechProps.Veh_Number,
COUNT(HTG_ScheduleRequest.ID) AS current_job
FROM HTG_TechProps
LEFT JOIN HTG_ScheduleRequest
ON HTG_TechProps.EmpNumber = HTG_ScheduleRequest.SSR
AND (HTG_ScheduleRequest.ScheduleDateCurrent = CURDATE())
AND HTG_ScheduleRequest.JobStatus = '3'
GROUP BY HTG_TechProps.EmpNumber
ORDER BY HTG_TechProps.EmpNumber ASC
假設EmpNumber
是唯一的,請嘗試以下版本(索引跟隨查詢):
SELECT tp.EmpNumber, tp.EmpFirstName, tp.EmpLastName, tp.Veh_Number,
(SELECT COUNT(*)
FROM HTG_ScheduleRequest sr
WHERE tp.EmpNumber = sr.SSR AND
sr.ScheduleDateCurrent = CURDATE() AND
sr.JobStatus = '3'
)
FROM HTG_TechProps tp
ORDER BY tp.EmpNumber ASC;
在運行查詢之前,請創建以下索引: HTG_TechProps(EmpNumber)
和HTG_ScheduleRequest(SSR, JobStatus, ScheduleDateCurrent)
。
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