每次查询PostgreSQL VIEWS是否新建？

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我正在创建一个具有一些复杂的底层关联的网络应用程序。为了解决我创建了一个UNION视图的几个问题。可能还有很多其他方法可以解决。

I am creating a web app which has some complex underlying associations. In order to solve several issues I was having I created a UNION View. There are probably a lot of other ways this could be solved.

但是，我正在考虑我的设计效率，我想知道一个VIEW是否新创建每次查询时，或者只创建一次，并保持更新。

But I am now considering the efficiency of my design, and I wanted to know if a VIEW is newly created each time it is queried, or is it only created once, and kept updated.

要详细说明，如果我有table_a（100条记录）和table_b（100条记录）和做一个UNION视图，然后我创建了一个包含200条记录的视图。

To elaborate, if I have table_a (100 records) and table_b (100 records) and make a UNION View, then I have created a view with 200 records.

这个整个过程是否每次对View进行选择？

Does this whole process occur each time I do a select against the View?

再次显示，每次更新底层表格记录时，视图都会更新，但视图是否会更新此记录，或者从头开始重新创建整个视图？

Again, obviously each time I update the underlying table records the view is updated, but does the view update this one record or does it recreate the whole view from scratch?

Dale

推荐答案

视图只不过是一个名称查询。有可能与perf相关的优化，一些DBMS实现比其他人更好（pgSQL似乎在更好的一面），如重用查询计划，缓存访问控制等。

A view is nothing more than a query with a name. There are possible perf-related optimizations, that some DBMS realize better than others (pgSQL seems to be on the better side), like reusing the query plan, cached access control etc.

然而，在他们这一天的结尾，几乎总是，你可以期待一个视图的行为就像直接发出SQL。有区别的是，您可以授予访问此查询的权限，允许访问底层表。

However, at the end of they day, almost always, you can expect a view to behave like issuing the SQL directly. With the difference that you can grant access to this query w/o granting access to the underlying tables.

有优化可以改变行为（使它们一半表格），这可能或可能不存在于pgSQL像物化视图（抱歉不知道关于pgSQL），但这只是nitpicking。

There are optimizations that you could do which change the behavior (make them half table-like) and that might or might not exist in pgSQL like materialized views (sorry no idea about pgSQL), but this is just nitpicking.