我有一个以下SQL语句应该返回月份，ph1，ph2和ph3值，其中下个月的最小值 - 上个月的最小值
SELECT DATE_FORMAT(a1.date_time, '%M,%Y') AS month,
(a4.ph1_active_energy)*10 - a1.ph1_active_energy AS 'ph1', (a4.ph2_active_energy)*10 - a1.ph2_active_energy AS 'ph2', (a4.ph3_active_energy)*10 - a1.ph3_active_energy AS 'ph3'
FROM powerpro a1
JOIN (SELECT MONTH(date_time) month, MIN(date_time) AS min FROM powerpro GROUP BY MONTH(date_time)
) a2 ON a1.date_time = a2.min
JOIN (SELECT MONTH(date_time) month, MIN(date_time) AS min FROM powerpro GROUP BY DATE(date_time)
) a3 ON DATE(a1.date_time) = a3.date - INTERVAL 1 DAY
JOIN powerpro
a4 ON a4.date_time = a3.min
WHERE YEAR(a1.date_time) = YEAR(CURDATE()) ORDER BY a1.date_time
我想只获得当年的记录。但脚本返回空结果集。
可能出现的问题。任何人都可以帮助我吗？