SELECT t1.a, t1.b, count(t1.b) FROM table1 AS t1
WHERE EXISTS(
SELECT 1 FROM 2table AS t2
WHERE t1.a = t2.a
AND t2.RTU代码=0
)
AND t1.b IN (0,2)
AND t1.SOC between 1465056000 AND 1465228800
GROUP BY a, b
ORDER BY NULL;#假如不需要排序的话，可以显式关闭排序

然后table1的SOC字段要建索引。

***还是用EXPLAIN分析一下SQL，看看哪里还有优化的地方（但凡涉及到GROUP BY的SQL性能都不太好）。