所有在sql中都为零的对

Question

I have 2 tables:

1. Pet_table , which contains an ID number and type of pet (eg 'cat')
2. Size_table , which contains an ID number and size ('S','M','L')

I want to print out how often the pairs occur, including zeros. For example:

id   Pet_Type         id    SIZE
   1    'cat'            1     'S'
   2    'cat'            2     'S'
   3    'cat'            3     'L'
   4    'dog'            4     'M'
   5    'snake'          5     'S'
   6    'dog'            6     'M'

From this example, I'd want:

cat   | S | 2 
cat   | M | 0 
cat   | L | 1
dog   | S | 0 
dog   | M | 2 
dog   | L | 0
snake | S | 1
snake | M | 0
snake | L | 0

I almost have the answer, but I can't seem to get the zeros to print out.

SELECT pet_type, size, COUNT(*) FROM pet_table LEFT JOIN size_table
ON pet_table.id=size_table.id GROUP BY pet_type,size;

Gives me:

cat   | S | 2 
cat   | L | 1
dog   | M | 2 
snake | S | 1

I'm at my wits end, so any help would be appreciated. Doing this in sqlite3 if that matters.

Answer 1

You need a driver table to get all possible combinations of pets and sizes and then use this for the joins:

SELECT pet_type, size, COUNT(st.id)
FROM (select distinct pet_type from pet_table) p cross join
     (select distinct size from size_table) s LEFT JOIN
     pet_table pt
     on pt.pet_type = p.pet_type left join
     size_table st
     ON pt.id=st.id and st.size = s.size
GROUP BY p.pet_type, s.size;

Answer 2

Try this:

select t1.pet_type, t1.size, ifnull(t2.[count], 0) [count]
from (
    select distinct p.pet_type, t.size
    from pet_table p
    cross join (select distinct size from size_table) t) t1
left join (
    SELECT p.pet_type, s.size, COUNT(*) [count]
    FROM pet_table p
    LEFT JOIN size_table s ON p.id=s.id 
    GROUP BY p.pet_type, s.size) t2 on t1.pet_type = t2.pet_type and t1.size = t2.size
order by t1.pet_type, t1.size

SQLFiddle