SQL语句

Question

如果我有下面这张表格：

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;

我希望能够得到一个表格，以显示最新版本的三个问题。这是在SQL Server 2005中实现的。

- SBurris

---

+1 表创建和插入语句。如果我正确理解了问题，似乎应该返回给定测试数据中的所有行。我建议包括那些将被正确查询排除的行。 - Shannon Severance

Answer 1

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;

- Cade Roux

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这就是它，但子查询中有一个额外的 ')' ，而 num 需要在 group by 中。 （无法编辑） - SBurris

Answer 2

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;

- Bill Karwin

Answer 3

你正在使用 SQL Server 2005，因此至少值得探索over子句：

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

- Eric

Answer 4

我想要一个表格来显示每个问题的最新三个版本。

1. 我假设qversion随时间递增。如果这个假设是错误的，请从答案中删除desc关键字。
2. 表定义没有在qversion上明确的非空约束。我假设空的qversion应该被排除在外。（注意：根据设置，声明中缺少显式的null/not null可能会导致非空约束。）如果表具有非空约束，则应删除文本where qversion is not null。如果qversion可以为空，并且需要将空值包含在结果集中，则需要进行其他更改。

---

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

- Shannon Severance