Coding guidelines

- For SQL statement, when using GROUP_CONCAT it's highly recommended to use | as separator. Because by default, most database use comma as a separator. When raw data is used for csv output; column cannot contain comma. 
For example, instead of 
SELECT GROUP_CONCAT(order_id) -- which yield 3,5,7 -> breaks the CSV download
we should do
SLECT GROUP_CONCAT(order_id  SEPARATOR '|') -- which yields 3|5|7 -> does not break for the CSV download