Question

例如，我有一个表test：

number   | text | date1      | date2
1        | a    | 2015-02-21 | 2015-02-23
1        | b    | 2015-02-22 | 2015-02-23
1        | c    | 2015-02-22 | 2015-02-24
1        | d    | 2015-02-21 | 2015-02-24
2        | a    | 2015-02-21 | 2015-02-21
2        | b    | 2015-02-22 | 2015-02-23

我需要最后显示每个数字date1和date2的文本。期望的结果集：

number   | text | date1      | date2
1        | c    | 2015-02-22 | 2015-02-24
2        | b    | 2015-02-22 | 2015-02-23

正确地工作SELECT：

SELECT
  *
FROM
  (SELECT
    *
  FROM
    test
  ORDER BY
    date1 DESC, date2 DESC
  ) as tab
GROUP BY
  number

这总是能正常工作吗？

是否始终显示第一行分组项目中的数据？

Answer 1

我不确定我是否达到目标，但请尝试此查询：

SELECT
  test.number,
  test.text,
  t1.date1,
  t1.date2,
FROM test
RIGHT JOIN
  (SELECT
    number, 
    MAX(date1) as date1,
    MAX(date2) as date2,
    MAX(CASE WHEN date2>=date1 THEN date2 ELSE date1 END) as dateMax
  FROM
    test
  GROUP BY number
  ) as t1
ON t1.number=test.number 
   AND (t1.dateMax = test.date1
   OR t1.dateMax = test.date2)

Mysql - group by总是显示第一行的列？

1 个答案: