postgres中的視圖和物化視圖

創建環境表　　

--創建表
CREATE TABLE teacher (
    id int NOT NULL,
    sname varchar(100)
);

CREATE TABLE student (
    sid int NOT NULL,
    teacher_id int NOT NULL DEFAULT 0,
    tname varchar(100)
);

INSERT into teacher(id,sname) SELECT id,id || 'lili' from generate_series(1,3) as id;

INSERT INTO student (sid,teacher_id,tname) SELECT id,tea,id || 'qqqv' from generate_series(1,4) as id , generate_series(1,3) as tea;

創建普通視圖

CREATE VIEW teacher_V as SELECT id,b.tname from teacher a JOIN student b ON a.id = b.teacher_id;

創建物化視圖

CREATE MATERIALIZED VIEW teacher_M as SELECT id,b.tname from teacher a JOIN student b ON a.id = b.teacher_id;

區別分析

　　01,插入數據

INSERT into student VALUES (10001,2,'lipeng');

　　02,普通視圖查看

SELECT * from teacher_V
   .....
    3    3qqqv
    1    4qqqv
    2    4qqqv
    3    4qqqv
    2    lipeng

　　03,物化視圖查看

SELECT * from teacher_M
......
3    3qqqv
1    4qqqv
2    4qqqv
3    4qqqv

　　04, 結果對比

　　　從結果上發現了問題,我插入了值, 普通視圖能直接獲取到,但是物化視圖缺不能獲取到

　　  05, 物化視圖如何獲取?

kingledb=# \help  refresh materialized view
Command:     REFRESH MATERIALIZED VIEW
Description: replace the contents of a materialized view
Syntax:
REFRESH MATERIALIZED VIEW [ CONCURRENTLY ] name
    [ WITH [ NO ] DATA ]

刷新物化視圖

　　　　

refresh MATERIALIZED VIEW teacher_M with no data;


--查詢--


SELECT * from teacher_M
> ERROR:  materialized view "teacher_m" has not been populated
HINT:  Use the REFRESH MATERIALIZED VIEW command.

發現刷新了這個報錯了?

    其實這個是no data的參數, 因為視圖進行了更改,你使用no data 刷新就會報錯,這個適用於 快速無數據刷新
    如果產生了數據的話需要使用 

refresh MATERIALIZED VIEW teacher_M with  data;

然后 查詢 就可以了

　　06, 查詢執行計划

EXPLAIN SELECT * from teacher_V;
Hash Join  (cost=17.20..156.66 rows=3024 width=11)
  Hash Cond: (b.teacher_id = a.id)
  ->  Seq Scan on student b  (cost=0.00..28.90 rows=1890 width=11)
  ->  Hash  (cost=13.20..13.20 rows=320 width=4)
        ->  Seq Scan on teacher a  (cost=0.00..13.20 rows=320 width=4)


EXPLAIN SELECT * from teacher_M
    Seq Scan on teacher_m  (cost=0.00..31.40 rows=2140 width=10)

　　　　會發現這個物化視圖直接視圖抽取結果,所以每次數據是特別塊出來的,普通視圖還會去每個表查詢

　　　07,場景分析

　　　　物化視圖適合的場景應該是對數據的實時性要求不高的場景。