SQL：查看表中值的函数

Question

我正在使用事务数据库：一种关系数据库，其中表中的行被定义为数据库在给定时间“认为”该行的字段包含的一组值。

部分架构：

CREATE TABLE Article
(
    id INTEGER,
    PRIMARY KEY(id)
);

CREATE TABLE Article_headline
(
    Article_id INTEGER,
    headline TEXT,
    tt DATETIME
    FOREIGN KEY(Article_id) REFERENCES Article(id)
);

CREATE TABLE Article_body
(
    Article_id INTEGER,
    body TEXT,
    tt DATETIME
    FOREIGN KEY(Article_id) REFERENCES Article(id)
);

换句话说，虚拟的“Article”表具有三列：id、headline 和 body。

我可以创建临时视图来表示给定时间定义的虚拟“文章”表：

CREATE TEMPORARY VIEW Article_headline_old
AS SELECT Article_id, headline, MAX(tt)
FROM Article_headline
WHERE tt <= "2011-11-03 16:05:23"
GROUP BY Article_id;

CREATE TEMPORARY VIEW Article_body_old
AS SELECT Article_id, body, MAX(tt)
FROM Article_body
WHERE tt <= "2011-11-03 16:05:23"
GROUP BY Article_id;

CREATE TEMPORARY VIEW Article_old
AS SELECT id, headline, body
FROM Article, Article_headline_old, Article_body_old
WHERE Article_headline_old.Article_id = Article.id
AND Article_body_old.Article_id = Article.id;

每次我想要查询数据库以获取文章时，我都必须创建这三个临时视图，但我宁愿不这样做。我更愿意创建永久视图“函数”作为模式本身的一部分：

CREATE VIEW Article_headline_at(theTime)
AS SELECT Article_id, headline, MAX(tt)
FROM Article_headline
WHERE tt <= theTime
GROUP BY Article_id;

CREATE VIEW Article_body_at(theTime)
AS SELECT Article_id, body, MAX(tt)
FROM Article_body
WHERE tt <= theTime
GROUP BY Article_id;

CREATE VIEW Article_at(theTime)
AS SELECT id, headline, body
FROM Article,
     Article_headline_at(theTime) AS Article_headline_old,
     Article_body_at(theTime) AS Article_body_old
WHERE Article_headline_old.Article_id = Article.id
AND Article_body_old.Article_id = Article.id;

然后当我想从数据库中选择一篇文章时：

SELECT * FROM Article_at("2011-11-03 16:05:23");

SQL 是否有类似的功能？

Answer 1

您可以创建三个存储过程并将 theTime 作为变量传递给每个存储过程。

对于 Article_headline_at 和 Article_body_old_at 将这些存储过程插入到 Article_at 存储过程内的临时表中并执行查询。这可能是你的解决方案：

CREATE PROCEDURE Article_headline_at @theTime datetime as

SELECT Article_id, headline, MAX(tt)
FROM Article_headline
WHERE tt <= theTime
GROUP BY Article_id;

-----



CREATE PROCEDURE Article_body_old_at @theTime datetime as
SELECT Article_id, body, MAX(tt)
FROM Article_body
WHERE tt <= theTime
GROUP BY Article_id;

-----

CREATE PROCEDURE Article_at @theTime datetime as
IF OBJECT_ID('tempdb.dbo.#Article_headline_at') IS NOT NULL DROP TABLE tempdb.dbo.#Article_headline_at
IF OBJECT_ID('tempdb.dbo.#Article_body_old_at') IS NOT NULL DROP TABLE tempdb.dbo.#Article_body_old_at

create table #Article_headline_at (
Article_id int,
body nvarchar(max),
tt int
)

create table #Article_body_old_at (
Article_id int,
headline nvarchar(max),
tt int
)

declare @sql1 nvarchar(max)
declare @sql2 nvarchar(max)

set @sql1 = 'insert into #Article_headline_at exec #Article_headline_at @theTime = '''+ @theTime + ''''
set @sql2 = 'insert into #Article_body_old_at exec #Article_body_old_at @theTime = '''+ @theTime + ''''

exec sp_executesql @sql1
exec sp_executesql @sql2


SELECT id, headline, body
FROM Article, #Article_headline_at(theTime), #Article_body_at(theTime)
WHERE #Article_headline_old.Article_id = Article.id
AND #Article_body_old.Article_id = Article.id;

-----

所以最后你能做的就是

exec Article_at @theTime = "2011-11-03 16:05:23"

但我确信有一个更简单的方法，但这是我能想到的唯一方法。