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What does refresh materialized view do?
REFRESH MATERIALIZED VIEW completely replaces the contents of a materialized view. To execute this command you must be the owner of the materialized view. The old contents are discarded. If WITH NO DATA is specified no new data is generated and the materialized view is left in an unscannable state.
Can we automate refresh of materialized views?
2 Answers. Yes, you can define a Materialized View with ON COMMIT , e.g.: CREATE MATERIALIZED VIEW sales_mv BUILD IMMEDIATE REFRESH FAST ON COMMIT AS SELECT t.
How do you quick refresh a materialized view?
For fast refresh to be possible, the SELECT list must contain all of the GROUP BY columns (if present), and there must be a COUNT(*) and a COUNT(column) on any aggregated columns. Also, materialized view logs must be present on all tables referenced in the query that defines the materialized view.
How do you refresh a materialized view in SQL?
The simplest form to refresh a materialized view is a Complete Refresh. It loads the contents of a materialized view from scratch. This means, if the SQL query of the materialized view has an execution time of two hours, the Complete Refresh takes at least two hours as well – or ofter even longer.
What is view in Snowflake?
Tables and views are the primary objects created and maintained in database schemas: All data in Snowflake is stored in tables. Views can be used to display selected rows and columns in one or more tables.
What are the refresh options in materialized view?
When you define a materialized view, you can specify three refresh options: how to refresh, what type of refresh, and can trusted constraints be used. If unspecified, the defaults are assumed as ON DEMAND, FORCE, and ENFORCED constraints respectively. The two refresh execution modes are ON COMMIT and ON DEMAND.
When is materialized view not compatible with base table?
When a materialized view is created on both base tables with timestamp-based materialized view logs and base tables with commit SCN-based materialized view logs, an error (ORA-32414) is raised stating that materialized view logs are not compatible with each other for fast refresh.
When to use trusted constraints in materialized view?
You can also specify if it is acceptable to use trusted constraints and REWRITE_INTEGRITY = TRUSTED during refresh. Any nonvalidated RELY constraint is a trusted constraint. For example, nonvalidated foreign key/primary key relationships, functional dependencies defined in dimensions or a materialized view in the UNKNOWN state.
How does atomic refresh work in materialized views?
Atomic refresh (TRUE or FALSE) If set to TRUE, then all refreshes are done in one transaction. If set to FALSE, then each of the materialized views is refreshed non-atomically in separate transactions.