# 语法参考
- 创建普通物化视图 基于SQL查询创建物化视图：
  ```
  CREATE MATERIALIZED VIEW [IF NOT EXISTS] view_name
  [(<col_name> [COMMENT <col_comment>], ...)]
  [COMMENT '...']
  [PARTITIONED BY col1, col2, ...]
  [ CLUSTERED BY (col_name3, col_name4, ...)
  [ SORTED BY (col_name [ ASC | DESC], ...)]
  INTO num_buckets BUCKETS]
  [TBLPROPERTIES ('key'='value', ...)]
  AS <SELECT query>;
  ```
  样例：
  ```
  CREATE MATERIALIZED VIEW mv_partitioned
  PARTITIONED BY (region, product)
  AS SELECT region, product, SUM(amount) AS total
  FROM sales GROUP BY region, product
  ```
  ```
  CREATE MATERIALIZED VIEW mv_sorted_bucketed
  CLUSTERED BY (id) SORTED BY (amount ASC) INTO 2 BUCKETS
  AS SELECT * FROM sales
  ```
  ```
  CREATE MATERIALIZED VIEW mv_sales_with_product AS
  SELECT s.region, p.product_name, SUM(s.amount) AS total_amount
  FROM sales s
  INNER JOIN products p ON s.product_id = p.product_id
  GROUP BY s.region, p.product_name
  ```
  
- 删除物化视图
  ```
  DROP MATERIALIZED VIEW [IF EXISTS] mv_revenue_per_customer;
  ```
  样例：
  ```
  DROP MATERIALIZED VIEW mv_sales
  ```
  
- 查询物化视图 查询当前数据库中的所有物化视图
  ```
  SHOW MATERIALIZED VIEWS;
  ```
  查询指定数据库中的所有物化视图
  ```
  SHOW MATERIALIZED VIEWS FROM example_db;
  ```
  查询符合特定模式的物化视图
  ```
  SHOW MATERIALIZED VIEWS LIKE 'mv_*';
  ```
  
- 刷新物化视图 从基表中重新计算物化视图的数据。
  ```
  REFRESH MATERIALIZED VIEW mv_revenue_per_customer;
  ```
  
- 修改物化视图属性
  ```
  ALTER MATERIALIZED VIEW mv_name SET TBLPROPERTIES ('key1' = 'val1');
  ```
  
- 删除物化视图属性
  ```
  ALTER MATERIALIZED VIEW mv_name UNSET TBLPROPERTIES ('key1' = 'val1');
  ```
  下列属性无法用Alter命令修改：
  - mv.archived：视图是否归档
  
  - mv.base.table.valid：视图是否可用于重写SQL
  
  - mv.base.tables：物化视图基表
  
  - mv.base.table.names：物化视图
  
  - mv.select.statement.spark：本物化视图在spark引擎中对应的select语句
  
  - mv.base.tables.last.update.time：物化视图基表最近刷新的时间
  
  - mv.last.refresh.time：物化视图最近刷新的时间
  
  - viewQuery：物化视图的查询语句
  
  - spark.mv.type：物化视图类型
  
  
  下列属性允许使用Alter命令修改
  mv.refresh.policy：物化视图刷新策略
  可使用下面语法修改刷新策略
  ```
  ALTER MATERIALIZED VIEW mv_altr ADD SCHEDULE REFRESH EVERY 3 DAYS
  ALTER MATERIALIZED VIEW mv_altr ALTER SCHEDULE REFRESH EVERY 2 DAYS
  ALTER MATERIALIZED VIEW mv_altr DROP SCHEDULE;
  ```