How to find only id that has different values in MySQL?

Question

I have a table with two columns:

id	num
1	2
2	8
1	7
7	3

I want to get as an answer to my query only ids that have more than 1 nums. For example in my table I would want to get as a result:

id
1

How should I express my query? Thanks in advance.

Answer 1

You might need something like this:

SELECT id
FROM your_table_name
GROUP BY id
HAVING count(DISTINCT num) > 1;

Google 'Aggregate functions'. Here the aggregate function is count() and it works always coupled with a GROUP BY clause. Pretty fun.