mysql表数据纵横转置sql语句

select student,
    sum(if(course='语文',mark,0)) as 语文,
    sum(if(course='数学',mark,0)) as 数学
from table1
group by student

1   a
2   b
1   c
2   d
合并为
1   a,c
2   b,d

select group_concat(column_b,separator ',') from table_name group by column_a;