遵义广告公司网站建设如何申请域名

40.3 物化视图

物化视图与视图类似，也适用规则系统，不过物化视图保留结果集。

CREATE MATERIALIZED VIEW mymatview AS SELECT * FROM mytab;

与

CREATE TABLE mymatview AS SELECT * FROM mytab;

之间，最主要的区别是物化视图不可直接被更新，需要刷新物化视图数据：

REFRESH MATERIALIZED VIEW mymatview;

假设有表：

CREATE TABLE invoice (
invoice_no integer PRIMARY KEY,
seller_no integer, -- ID of salesperson
invoice_date date, -- date of sale
invoice_amt numeric(13,2) -- amount of sale
);

如果需要查看数据汇总，但无需最新数据，则可创建物化视图：

CREATE MATERIALIZED VIEW sales_summary AS
SELECT
seller_no,
invoice_date,
sum(invoice_amt)::numeric(13,2) as sales_amt
FROM invoice
WHERE invoice_date < CURRENT_DATE
GROUP BY
seller_no,
invoice_date
ORDER BY
seller_no,
invoice_date;CREATE UNIQUE INDEX sales_summary_seller
ON sales_summary (seller_no, invoice_date);

访问物化视图数据较表或视图更快，但需要定期刷新数据到物化视图中。