SQL语句

如果我有下表：

CREATE TABLE #temp (
    id int,
    num int,
    question varchar(50),
    qversion int );

INSERT INTO #temp VALUES(1, 1, 'Question 1 v1', 1);
INSERT INTO #temp VALUES(2, 1, 'Question 1 v2', 2);
INSERT INTO #temp VALUES(3, 2, 'Question 2 v1', 1);
INSERT INTO #temp VALUES(4, 2, 'Question 2 v2', 2);
INSERT INTO #temp VALUES(5, 2, 'Question 2 v3', 3);
INSERT INTO #temp VALUES(6, 3, 'Question 3 v1', 1);

SELECT *
FROM #temp;

DROP TABLE #temp;

---

我想要一个表格来显示这三个问题的最新版本？这是在SQL Server 2005中，您正在使用SQL Server 2005，因此至少值得探讨以下条款：

CREATE TABLE #temp (
    id int,
    num int,
    question varchar(50),
    qversion int );

INSERT INTO #temp VALUES(1, 1, 'Question 1 v1', 1);
INSERT INTO #temp VALUES(2, 1, 'Question 1 v2', 2);
INSERT INTO #temp VALUES(3, 2, 'Question 2 v1', 1);
INSERT INTO #temp VALUES(4, 2, 'Question 2 v2', 2);
INSERT INTO #temp VALUES(5, 2, 'Question 2 v3', 3);
INSERT INTO #temp VALUES(6, 3, 'Question 3 v1', 1);

WITH latest AS (
   SELECT num, MAX(qversion) AS qversion
   FROM #temp
   GROUP BY num
)
SELECT #temp.*
FROM #temp
INNER JOIN latest
    ON latest.num = #temp.num
    AND latest.qversion = #temp.qversion;

DROP TABLE #temp;

我想要一个表格来显示每个问题的三个最新版本

我假设qversion随着时间的推移而增加。如果此假设是反向的，请从答案中删除desc关键字。 表定义在qversion上没有显式的NOTNULL约束。我假设应该排除空的qversion。注意：根据设置，声明中缺少显式null/not null可能会导致not null约束。如果表中有not null CONTAint，则应删除qversion not null的文本。如果qversion可以为null，并且结果集中需要包含null，那么需要进行额外的更改。

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就是这样，但是子查询中有一个额外的num，num需要位于group by中。无法编辑表create和insert语句的+1。但是，如果我正确理解了这个问题，那么似乎应该返回给定测试数据中的所有行。我建议包含将被正确查询排除的行。

SELECT t1.id, t1.num, t1.question, t1.qversion
FROM #temp t1
LEFT OUTER JOIN #temp t2
  ON (t1.num = t2.num AND t1.qversion < t2.qversion)
GROUP BY t1.id, t1.num, t1.question, t1.qversion
HAVING COUNT(*) < 3;

select
    *
from
    (select *, max(qversion) over (partition by num) as maxVersion from #temp) s
where
    s.qversion = s.maxVersion

CREATE TABLE #temp (
    id int,
    num int,
    question varchar(50),
    qversion int );

INSERT INTO #temp VALUES(1, 1, 'Question 1 v1', 1);
INSERT INTO #temp VALUES(2, 1, 'Question 1 v2', 2);
INSERT INTO #temp VALUES(3, 2, 'Question 2 v1', 1);
INSERT INTO #temp VALUES(4, 2, 'Question 2 v2', 2);
INSERT INTO #temp VALUES(5, 2, 'Question 2 v3', 3);
INSERT INTO #temp VALUES(7, 2, 'Question 2 v4', 4); 
-- ^^ Added so at least one row would be excluded.
INSERT INTO #temp VALUES(6, 3, 'Question 3 v1', 1);
INSERT INTO #temp VALUES(8, 4, 'Question 4 v?', null);

select id, num, question, qversion
from (select *, 
        row_number() over (partition by num order by qversion desc) as RN
    from #temp
    where qversion is not null) T
where RN <= 3