How to correctly count the number of unique values ​​in a field in a query?

Question

SQL

Good afternoon.
There is a table table1 with fields id, name, size.
In the size field, the values ​​are text. You need to count and display the number of unique values.
For example, we have such values ​​as small, medium, large, medium, large, very large. Should get 4 as a result.
I tried with such a construction, but it gives 0.
SELECT SUM(DISTINCT size) FROM `table1`;

Answer 1

SELECT COUNT(DISTINCT size) FROM table1