mysql min ignores null - need workaround/tweak

Question

For this query

SELECT min(date) min_date FROM  order_products group by order_id

min_date ignores the NULL values in a group of order id.

In my case I want min_date = NULL if the group has a order_products tuple with null value in date.

Any idea how can I achieve this ?

Answer 1

A simple workAround could be:

SELECT min(IFNULL(date, '1970-01-01')) AS min_date 
FROM order_products 
GROUP BY order_id

So, if 1970/01/01 turns up, you know that there's a NULL value.

Answer 2

select case when count(date)=sum(1) then min(date) else null end

or, when all rows are not null, return min date, else return null.