sql语句，按一个字段中的值当作结果列，列出表数据，如图

select year ,count(m1) m1,count(m2) m2,count(m3) m3,count(m4) m4 from (select year , count(1) m1,0 m2,0 m3, 0 m4 from tab where month='1' group by year union all select year , 0 m1,count(1) m2,0 m3, 0 m4 from tab where month='2' gro