MATERIALIZED VIEW
PG 9.3 版本之后开始支持物化视图。
View 视图：
虚拟，不存在实际的数据，在查询视图的时候其实是对视图内的表进行查询操作。
物化视图：
实际存在，将数据存成一张表，查询的时候对这个表进行操作。物化视图内的数据需要和表的数据进行同步，这就是refresh。
实验环境：
CentOS 7
PG 10.4
操作实验：
初始化环境：
创建表，并插入数据
mytest=# create table t1 (id int ,col1 varchar(10),col2 varchar(10));
mytest=# create table t2 (id int ,col3 varchar(10), col4 varchar(10), col5 varchar(10));
mytest=# insert into t1 values (1,'a','b'); ......
mytest=# insert into t2 values (1,'c','d','e'); ......
mytest=# select * from t1;
id | col1 | col2
----+------+------
1 | a | b
2 | a | b
3 | a | b
4 | a | b
5 | a | b
(5 rows)
mytest=# select * from t2;
id | col3 | col4 | col5
----+------+------+------
1 | c | d | e
2 | c | d | e
3 | c | d | e
4 | c | d | e
5 | c | d | e
(5 rows)
创建物化视图：
CREATE MATERIALIZED VIEW IF NOT EXISTS mv_t1_t2 (t1_id,t2_id, col1,col2,col3,col4,col5)
AS
SELECT t1.id, t2.id, t1.col1,t1.col2,t2.col3,t2.col4,t2.col5 from t1,t2
where t1.id = t2.id
WITH DATA;
mytest=# select * from mv_t1_t2;
t1_id | t2_id | col1 | col2 | col3 | col4 | col5
-------+-------+------+------+------+------+------
1 | 1 | a | b | c | d | e
2 | 2 | a | b | c | d | e
3 | 3 | a | b | c | d | e
4 | 4 | a | b | c | d | e
5 | 5 | a | b | c | d | e
(5 rows)
刷新物化视图：
mytest=# insert into t1 values (11,'x','y');
mytest=# insert into t2 values (11,'x','y','z');
对表进行操作，不改变物化视图中的数据。查询物化视图，数据没有改变
mytest=# select * from mv_t1_t2 ;
t1_id | t2_id | col1 | col2 | col3 | col4 | col5
-------+-------+------+------+------+------+------
1 | 1 | a | b | c | d | e
2 | 2 | a | b | c | d | e
3 | 3 | a | b | c | d | e
4 | 4 | a | b | c | d | e
5 | 5 | a | b | c | d | e
(5 rows)
全量更新：
刷新物化视图才能使物化视图的数据改变。
mytest=# REFRESH MATERIALIZED VIEW mv_t1_t2 WITH DATA;
mytest=# SELECT * FROM mv_t1_t2 ;
t1_id | t2_id | col1 | col2 | col3 | col4 | col5
-------+-------+------+------+------+------+------
1 | 1 | a | b | c | d | e
2 | 2 | a | b | c | d | e
3 | 3 | a | b | c | d | e
4 | 4 | a | b | c | d | e
5 | 5 | a | b | c | d | e
11 | 11 | x | y | x | y | z
(6 rows)
增量更新
只有当物化视图中存在unique index的时候，refresh物化视图才能使用增量更新，加入concurrently参数。否则报错。
mytest=# REFRESH MATERIALIZED VIEW CONCURRENTLY mv_t1_t2 WITH DATA;
ERROR: cannot refresh materialized view "public.mv_t1_t2" concurrently
HINT: Create a unique index with no WHERE clause on one or more columns of the materialized view.
mytest=# create unique index uidx_mv_id on mv_t1_t2 (t1_id );
mytest=# REFRESH MATERIALIZED VIEW CONCURRENTLY mv_t1_t2 WITH DATA;
mytest=# insert into t1 values (12,'xx','yy');
mytest=# insert into t2 values (12,'xx','yy','zz');
mytest=# REFRESH MATERIALIZED VIEW CONCURRENTLY mv_t1_t2 WITH DATA;
mytest=# select * from mv_t1_t2 ;
t1_id | t2_id | col1 | col2 | col3 | col4 | col5
-------+-------+------+------+------+------+------
1 | 1 | a | b | c | d | e
2 | 2 | a | b | c | d | e
3 | 3 | a | b | c | d | e
4 | 4 | a | b | c | d | e
5 | 5 | a | b | c | d | e
11 | 11 | x | y | x | y | z
12 | 12 | xx | yy | xx | yy | zz
(7 rows)
物化视图刷新WITH NO DATA ,查询会报错
mytest=# REFRESH MATERIALIZED VIEW mv_t1_t2 WITH NO DATA;
mytest=# select * from mv_t1_t2 ;
ERROR: materialized view "mv_t1_t2" has not been populated
HINT: Use the REFRESH MATERIALIZED VIEW command.
mytest=# REFRESH MATERIALIZED VIEW mv_t1_t2 WITH DATA;
REFRESH MATERIALIZED VIEW
mytest=# select * from mv_t1_t2 ;
t1_id | t2_id | col1 | col2 | col3 | col4 | col5
-------+-------+------+------+------+------+------
1 | 1 | a | b | c | d | e
2 | 2 | a | b | c | d | e
3 | 3 | a | b | c | d | e
4 | 4 | a | b | c | d | e
5 | 5 | a | b | c | d | e
11 | 11 | x | y | x | y | z
12 | 12 | xx | yy | xx | yy | zz
(7 rows)
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作者：Chuck_Chen1222
