介绍PostgreSQL中的视图和物化视图的差异。

举个例子：查看系统中的所有的用户表：
基本查询是这样的

select * from pg_class where relnamespace != '11' and relnamespace != '13887'  and relkind = 'r'

写成视图格式

CREATE VIEW "public"."v_user_tab"
AS
select * from pg_class where relnamespace != '11' and relnamespace != '13887'  and relkind = 'r';

写成物化视图格式

CREATE MATERIALIZED VIEW "public"."mv_user_tab"
AS
select * from pg_class where relnamespace != '11' and relnamespace != '13887'  and relkind = 'r';