题解 | #when：判断其是否有过购买记录#

#两种方式（if和when）

# if要熟悉
#select customer_id ,if(latest_place_order_date is null,0,1) as if_placed_order from customers_info

# when方式
select 
customer_id,
(case    when latest_place_order_date is null then 0
         when latest_place_order_date is not null then 1 
end ) as "if_placed_order"
from customers_info

#或 更简单的用else

# select 
# (customer_id,
# case    when latest_place_order_date is null then '0'
#         else 1
# end ) as "if_placed_order"
# from customers_info