如何使用mysql中的月和年表列（int）获取最旧的条目（月-年）？

Question

我有一个表格，其中一列保留年份，另一列保留月份。 如何按son_id 获得最旧的日期（最小td_month-td_year）分组？ 注意事项：table_id 可能不按顺序

CREATE TABLE mytable (
table_id INT,  
father_id INT, 
son_id INT, 
mt_month INT, 
mt_year INT);

INSERT INTO mytable VALUES
("101","11","370","12","2013"),
("102","11","370","1","2014"),
("103","11","371","2","2015"),
("105","11","371","11","2008"),
("107","11","371","12","2008"),
("108","11","372","2","2009"),
("109","11","372","3","2009"),
("111","11","372","12","2009"),
("113","11","373","1","2013"),
("115","11","373","11","2017"),
("117","11","373","11","2011"),
("119","11","373","12","2012");

如果不考虑年份，此查询将出错月份：

select son_id, min(mt_month), min(mt_year) from mytable group by son_id;

https://www.db-fiddle.com/f/v1Xty9c1SAp2PfaWCC4WvK/3

我应该使用 concat mt_month 和 mt_year 并将其转换为日期格式吗？

Answer 1

您需要先获得最小年份：

SELECT y.son_id,y.min_year,min(t.mt_month) AS min_month
FROM mytable t
INNER JOIN (
  select son_id,  min(mt_year) AS min_year from mytable group by son_id) y
ON t.son_id=y.son_id
AND t.mt_year=y.min_year
GROUP BY y.son_id,y.min_year;

Answer 2

如果您想要每年的第一个月，那么您需要对年份进行分组，以找到每年的最小月份，然后再进行第二个分组。

select son_id, month, year
from (
  select son_id, min(mt_month) AS month, min(mt_year) as YEAR
  from mytable 
  group by son_id,mt_year) x
group by son_id
;