Most efficient way to output a large table to multiple csv file based on column value

I have a 1 GB table, I need to output the db to multiple csv files based on column value. For instance:

c1              |   c2                  |   c3

1               |   a                   |   100    
2               |   b                   |   102    
3               |   a                   |   103    
4               |   b                   |   104

to be:

a.csv

1               |   a                   |   100    
3               |   a                   |   103

b.csv

2               |   b                   |   102
4               |   b                   |   104

considering the size of table, what's the most efficient way to do this?

Update: so far I have been able to do select * from table_name order by c2; and .mode csv .out a.csv select * from table_name; on a smaller sample of the dataset. I was wondering what are alternative except looping through all item manually.