Question

For example I have table that has such columns as geography and children. I need to count how many there are childrens from each country.

I only could make such thing:

SELECT geography, COUNT( * ) 
FROM table1
GROUP BY children
ORDER BY geography

Well, I have for example:

Canada John
Canada John
Canada Peter

I need result such as from Canada there are 2 children.
But If I will make group by children there result is:

Canada 2
Canada 1

If group by geography then,

Canada 3

Answer 1

If you need to count only the unique values in a group, you can use COUNT(DISTINCT expr)

SELECT geography, COUNT(DISTINCT children) 
FROM table1
GROUP BY geography
ORDER BY geography