MySQL の COUNT DISTINCT

SELECT COUNT(DISTINCT COLUMN_NAME)
FROM TABLE_NAME;

SELECT COUNT(*) AS rows_total, COUNT(DISTINCT rating) AS ratings FROM film;

+------------+---------+
| rows_total | ratings |
+------------+---------+
|       1000 |       5 |
+------------+---------+
1 row in set (0.01 sec)

SELECT COUNT(DISTINCT rating, rental_rate) AS combinations FROM film;

+--------------+
| combinations |
+--------------+
|           15 |
+--------------+
1 row in set (0.00 sec)

SELECT COUNT(*) AS rows_total,
       COUNT(DISTINCT address2) AS distinct_values
FROM address;

+------------+-----------------+
| rows_total | distinct_values |
+------------+-----------------+
|        603 |               1 |
+------------+-----------------+
1 row in set (0.00 sec)