-- 借楼上语句
-- 如果只要 C 表中的一列数据,可以使用标量子查询
SELECT A.*, B.* , (select max(c.Time) from C where b.Devicecode=c.Devicecode)
FROM 表B b JOIN 表A a ON b.A_ID=a.A_ID
SELECT MAX(a.A_name),MAX(b.B_name),MAX(c.Time) AS TIME,MAX(b.Devicecode)
FROM 表B b JOIN 表A a ON b.A_ID=a.A_ID
LEFT JOIN Data c ON b.Devicecode=c.Devicecode
WHERE b.A_ID=2
GROUP BY b.A_id,b.B_id;