N
SELECT COUNT (DISTINCT column-name) FROM table-name
N
SELECT DISTINCT Column_name FROM table_name;
N
SELECT DISTINCT column1, column1, ..... FROM TABLE
/*DISTINCT WILL NOT SELECT THE SAME VALUES IN SAME COLUMN*/
N
SELECT a.*
FROM emails a
INNER JOIN
(SELECT email,
MIN(id) as id
FROM emails
GROUP BY email
) AS b
ON a.email = b.email
AND a.id = b.id;