Find distinct Emails based on user column - mysql

Question

I'm trying to figure out how to find first occurrence of distinct Emails based on user column ordered by time, so assume my table is like this
| User | Email | | Time| |ID|
| David | 1 | | 2012/01/19 | |1|
| David | 2 | | 2012/01/20 | |2|
| David | 2 | | 2012/01/21 | |1|
| David | 2 | | 2012/01/22 | |2|
| David | 2 | | 2012/01/23 | |1|
| David | 3 | | 2012/01/24 | |2|
| David | 3 | | 2012/01/25 | |1|
| John | 1 | | 2012/01/19 | |1|
| John | 1 | | 2012/01/20 | |2|
| John | 1 | | 2012/01/21 | |1|
| John | 2 | | 2012/01/22 | |2|
| John | 2 | | 2012/01/23 | |1|
I want the result to look like this
| User | Email | | Time| |ID|
| David | 1 | | 2012/01/19 | |1|
| David | 2 | | 2012/01/20 | |2|
| David | 3 | | 2012/01/24 | |2|
| John | 1 | | 2012/01/19 | |1|
| John | 2 | | 2012/01/22 | |2|
What would be a good way to do this in MySQL? Distinct wouldn't work since it applies to all rows. I tried ROW_NUMBER() OVER (PARTITION BY Email ORDER BY Time DESC) rnm but this also doesn't work, as if you do rnm = 1 it ignores all the following emails (and rnm between 1 and 10 would return duplicates). I'm not sure if there's a way to group this based on a different email from the same user

Answer 1

You need to PARTITION BY User, Email. Also, to get the first occurrence, you need to order ascending, not descending.
WITH t AS (
SELECT *, ROW_NUMBER() OVER (PARTITION BY User, Email ORDER BY Time ASC) AS rn
FROM yourTable
)
SELECT User, Email, Time, ID
FROM t
WHERE rn = 1
DEMO
You would only need the window function if you want other columns from the same row as the minimum time.