SQL: How to find min value per group in sql? - mysql

Question

I have the following table snapshots:
domain year month day
--- --- --- ---
google 2007 04 15
google 2005 08 31
google 2005 12 01
facebook 2006 04 15
facebook 2006 02 25
facebook 2008 01 01
What I want to retrieve is the first (earliest) date of each domain.
So the output should be:
google 2005 08 31
facebook 2006 02 25
I have tried the following query, but it retrieves the minimum value for each column:
select domain, min(year), min(month), min(day) from snapshots group by domain

Answer 1

As mentioned you should use concatenation to create a single date and then select the lowest value.
select domain, MIN(CAST(CONCAT(`year`, '-'`,month`,'-',`day`) AS DATE)) from snapshots group by domain
Haven't tested this but this should give you an idea.

Answer 2

You can concatenate the values from the date field, cast them as date and select the min date (i expect the values to be varchar in this case):
SELECT domain,
MIN(CAST(CONCAT(year,'-',month,'-',day) AS date))
FROM snapshots
GROUP BY domain;

Answer 3

In MySQL:
SELECT
domain,
FROM_UNIXTIME(UNIX_TIMESTAMP(MIN(CONCAT(year,'-',month,'-',day))), '%Y') as y,
FROM_UNIXTIME(UNIX_TIMESTAMP(MIN(CONCAT(year,'-',month,'-',day))), '%m') as m,
FROM_UNIXTIME(UNIX_TIMESTAMP(MIN(CONCAT(year,'-',month,'-',day))), '%d') as d
FROM snapshots
GROUP BY domain;

Answer 4

There might be easier solutions, but you can create a new column of date type from the three columns year, month, and day. Then get the min date as following:
SELECT DISTINCT s.domain, s.year, s.month, s.day
FROM
(
SELECT domain, year,month,day,
STR_TO_DATE(CONCAT(`year`,'-',LPAD(`month`,2,'00'),'-',LPAD(`day`,2,'00')) ,'%Y-%m-%d') AS FullDate
FROM snapshots
) AS s
INNER JOIN
(
SELECT domain, MIN(Fulldate) MinDate
FROM
(
SELECT domain, year,month,day,
STR_TO_DATE(CONCAT(`year`,'-',LPAD(`month`,2,'00'),'-',LPAD(`day`,2,'00')) ,'%Y-%m-%d') AS FullDate
FROM snapshots
) AS t
GROUP BY domain
) AS t ON t.MinDate = s.FullDate
AND t.Domain = s.Domain;
demo
This will give you the exact results that you want:
| domain | year | month | day | MinDate |
|----------|------|-------|-----|------------|
| google | 2005 | 8 | 31 | 2005-08-31 |
| facebook | 2006 | 2 | 25 | 2006-02-25 |

Answer 5

Can you try this please and let me know if it solves your problem without concatenation? Could be made more robust with subqueries if necessary.
CREATE TABLE domainDate(domain CHAR(25), `year` INT, `month` INT, `day` INT);
INSERT INTO domainDate VALUES
('google', 2007, 04, 15),
('google', 2005, 08, 31),
('google', 2005, 12, 01),
('facebook', 2006, 04, 15),
('facebook', 2006, 02, 25),
('facebook', 2008, 01, 01);
SET #VDomain := '';
SELECT domain, `year`, `month`, `day` FROM domainDate HAVING #VDomain != #VDomain := domain ORDER BY domain, `year` * 10000 + `month` * 100 + `day`;
Thanks,
James

Answer 6

You can try ranking function ROW_NUMBER()
CREATE TABLE domainDate(domain CHAR(25), [year] INT, [month] INT, [day] INT);
INSERT INTO domainDate VALUES
('google', 2007, 04, 15),
('google', 2005, 08, 31),
('google', 2005, 12, 01),
('facebook', 2006, 04, 15),
('facebook', 2006, 02, 25),
('facebook', 2008, 01, 01);
SELECT domain
,[year]
,[month]
,[day]
FROM
(
SELECT domain
,[year]
,[month]
,[day]
,ROW_NUMBER() OVER(PARTITION BY domain ORDER BY [year], [month], [day]) AS RN
FROM domainDate
) t
WHERE RN = 1