How to get the count of each distinct value in a column?

I have an SQL table called "posts" that looks like this: id | category ----------------------- 1 | 3 2 | 1 3 | 4 4 | 2 5 | 1 6 | 1 7 | 2 Each category number corresponds to a category. How would I go about counting the number of times each category appears on a post all in **one SQL query**? As an example, such a query might return a symbolic array such as this: `(1:3, 2:2, 3:1, 4:1)` My current method is to use queries for each possible category, such as: `SELECT COUNT(*) AS num FROM posts WHERE category=#`, and then combine the return values into a final array. However, I'm looking for a solution that uses only one query.