SQL查询提供一列中的不同值，以及第二列中的不同值的计数

Question

Say I have a table like this:

column1 | column2
---------------------
1       | a
1       | b
1       | c
2       | a
2       | b

I need an SQL query to show the distinct values from column 1, and a count of the related distinct values from column 2. The output would look like:

column1 | count
-------------------
1       | 3
2       | 2

Answer 1

You could do something like this:

SELECT column1, count(column2)
FROM table
GROUP BY column1

Answer 2

You should do a COUNT(DISTINCT ...) with a GROUP BY :

Select    Column1,
          Count(Distinct Column2) As Count
From      Table
Group By  Column1