$statusQ = "SELECT COUNT(total_submit_sub) AS noofsub
FROM total_noof_sub
WHERE sub_name = 'PHP'
AND sem = '8'
AND dept = 'CE'
AND laborlec = 'Lab'
AND faculty_name = 'user'
AND convert(DATETIME,adate) BETWEEN Convert(DATETIME,CASE WHEN isnull(2019/01/01,'')='' THEN adate ELSE isnull(2019/01/01,'') END)
AND Convert(DATETIME, CASE WHEN isnull(2019/03/30,'')='' THEN adate ELSE isnull(2019/03/30,'') END)
Пожалуйста, попробуйте этот код, NULL Часть также обрабатывать ....
Спасибо !!!!!!