Question

我有下表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

我想要检索的是每个域的第一个（最早的）日期。

所以输出应该是：

google    2005  08  31
facebook  2006  02  25

我尝试了以下查询，但它检索每列的最小值：

select domain, min(year), min(month), min(day) from snapshots group by domain

Answer 1

如上所述，您应该使用串联来创建单个日期，然后选择最低值。

select domain, MIN(CAST(CONCAT(`year`, '-'`,month`,'-',`day`) AS DATE)) from snapshots group by domain

Haven没有对此进行测试，但这应该会给你一个想法。

Answer 2

您可以连接日期字段中的值，将它们转换为日期并选择最小日期（我希望在这种情况下值为varchar）：

SELECT domain, 
MIN(CAST(CONCAT(year,'-',month,'-',day) AS date)) 
FROM snapshots 
GROUP BY domain;

Answer 3

在MySQL中： 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

可能有更简单的解决方案，但您可以从年，月，日三列创建新的日期类型列。然后得到如下的最短日期：

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

这将为您提供所需的确切结果：

|   domain | year | month | day |    MinDate |
|----------|------|-------|-----|------------|
|   google | 2005 |     8 |  31 | 2005-08-31 |
| facebook | 2006 |     2 |  25 | 2006-02-25 |

Answer 5

请你试试这件事，让我知道它是否解决了你的问题而没有连接？如有必要，可以使用子查询使其更加健壮。

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`;

谢谢，

詹姆斯

Answer 6

您可以尝试排名函数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

SQL：如何在sql中找到每组的最小值？

6 个答案: