学步园

a表       	a              b
                123        10
                123        12
                1234      11
                1234      14

select * from a group by id

结果就是  id   a			b
                  1 123		10
                  2 1234		11

select a,group_concat(b order by id desc )from a group by id

结果就是  id   a			b
                  1 123		10,12
                  2 1234		11,14