如何给基于output的查询结果添加分类？

Question

Extending this question for a more general case:

I have a table called fruits with a column fruit that has three possible values: apple , orange , and mango . I used the following query to get the counts of each fruit by date :

SELECT date, fruit, COUNT(id) AS count
FROM fruits
WHERE date BETWEEN '2020-10-02' AND '2020-10-05'
GROUP BY date, fruit

that gives the following results:

date           fruit      count
--------------------------------
2020-10-02     apple        3
2020-10-02     orange       5
2020-10-03     orange       23
2020-10-03     mango        1
2020-10-04     mango        9
2020-10-05     apple        10
2020-10-05     orange       7
2020-10-05     mango        6

As you can see, not every date contains each type of fruit . Is it possible, and if so, how, to add the missing fruit by each date to the above results with a default count=0 , as shown below?

date           fruit      count
--------------------------------
2020-10-02     apple        3
2020-10-02     orange       5
2020-10-02     mango        0
2020-10-03     orange       23
2020-10-03     mango        1
2020-10-03     apple        0
2020-10-04     mango        9
2020-10-04     apple        0
2020-10-04     orange       0
2020-10-05     apple        10
2020-10-05     orange       7
2020-10-05     mango        6

Answer 1

Use a cross join ot generate the row and then a left join to bring in the results:

select d.date, f.fruit, coalesce(ff.count, 0) as count
from (select distinct date from fruits) d cross join
     (select distinct fruit from fruits) f left join
     fruits ff
     on ff.date = d.date and ff.fruit = f.fruit;