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ALTER MATERIALIZED VIEW [db_name.]materialized_view_name ENABLE|DISABLE REWRITE;

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Hive supports two types of rewriting algorithms:

• Algebraic: this is part of Apache Calcite and it supports queries

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• containing TableScan, Project, Filter, Join, and Aggregate operators. More information about

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• this rewriting coverage can be

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• found here. In the following, we include a few examples that briefly illustrate different rewritings.

Example 1

Consider the database schema created by the following DDL statements:

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SELECT floor(time to month),
    SUM(c_added)
FROM mv3
GROUP BY floor(time to month);

• SQL text: The materialized view definition query text is compared to the incoming query text or it's subquery text. It supports all kind of operators and aggregate functions.

Materialized view maintenance

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By default, Hive will attempt to rebuild a materialized view incrementally, falling back to full rebuild if it is not possible.

Current  Current implementation only supports incremental rebuild when there were were INSERT operations over the source tables, while UPDATE and DELETE operations will force a full rebuild of the materialized view.

To execute incremental maintenance, following conditions should be met :if there were only INSERT operations over the source tables:

• The materialized view should only use transactional tables (the source tables must be transactional), either micromanaged or ACID or a storage format that supports snapshots (ex. Iceberg)
• If the materialized view definition contains a Group By clause, the materialized view should be stored in an ACID table or a storage format that supports snapshots (ex. Iceberg v2), since it needs to support MERGE operation. For materialized view definitions consisting of Scan-Project-Filter-Join, this restriction does not exist.

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• If the materialized view definition contains a Group By clause the following aggregate functions are supported: COUNT, SUM, AVG (only if both COUNT and SUM defined for the same column), MIN, MAX

If there were UPDATE and DELETE operations over the source tables:

• The materialized view should only use transactional tables (the source tables must be transactional), either micromanaged or ACID
• The materialized view definition must contain a Group By clause and a COUNT(*) function call.
• The materialized view should be stored in an ACID table or a storage format that supports snapshots (ex. Iceberg v2), since it needs to support MERGE operation.   
• The following aggregate functions are supported: COUNT, SUM, AVG (only if both COUNT and SUM defined for the same column)

A rebuild operation acquires an exclusive write lock over the materialized view, i.e., for a given materialized view, only one rebuild operation can be executed at a given time.

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