Question

table1有3列：

Id UserName SubmittedDate
1 Joe 1/1/2006
2 Joe 1/1/2007
3 Nat 1/1/2008
4 Pat 1/1/2009

我想要归还：

Id用户名
2乔
3 Nat 4帕特

我只想要一张Joe的记录，最近的记录。

如何撰写此查询？感谢

Answer 1

SELECT  Id, UserName, SubmittedDate
FROM    (
        SELECT  Id, UserName, SubmittedDate,
                ROW_NUMBER() OVER (PARTITION BY UserName ORDER BY SubmittedDate DESC) rn
        FROM    table1
        ) q
WHERE rn = 1

Answer 2

SELECT MAX(ID), UserName
FROM table
GROUP BY UserName

请注意，这假设较高的ID意味着以后。它不直接在“提交日期”字段中查询。为此，使用Quassnoi更为复杂的一个：）

Answer 3

仅使用标准SQL：

SELECT Id, UserName
FROM table1
JOIN (
    SELECT UserName, MAX(SubmittedDate) AS MaxDate
    FROM table1
    GROUP BY UserName
    ) AS MaxDateTable ON table1.UserName = MaxDateTable.UserName
WHERE SubmittedDate = MaxDate

Answer 4

以下是三种可能的解决方案。给他们一个尝试，看看哪个更适合您的数据和情况。请注意，在用户名具有两个相同的submitted_date值的情况下，结果可能与您期望的不同。

SELECT
    T1.id,
    T1.username
FROM
    My_Table T1
INNER JOIN 
  (
   SELECT username, MAX(submitted_date) 
   FROM My_Table T2 GROUP BY username
  ) SQ 
    ON SQ.username = T1.username AND SQ.submitted_date = T1.submitted_date

SELECT
    T1.id,
    T1.username
FROM
    My_Table T1
WHERE
    NOT EXISTS 
    (
      SELECT * 
      FROM
         My_Table T2 
      WHERE
         T2.username = T1.username AND
         T2.submitted_date > T1.submitted_date
    )

SELECT
    T1.id,
    T1.username
FROM
    My_Table T1
LEFT OUTER JOIN My_Table T2 ON
    T2.username = T1.username AND
    T2.submitted_date > T1.submitted_date
WHERE
    T2.id IS NULL

Answer 5

扯掉@Quassnoi，但我喜欢传授使用CTEs来代替子查询和大多数视图。

WITH
query1 as(
    SELECT  Id, UserName, SubmittedDate,
            ROW_NUMBER() OVER (PARTITION BY UserName ORDER BY SubmittedDate DESC) rn
    FROM    table1
        )

SELECT  Id, UserName, SubmittedDate
FROM   query1
WHERE rn = 1

如何编写这个SQL语句

5 个答案: