6 aggregate functions. There is also a special type of query called recursive query. In SQL, it goes with Common Table Expression (CTE). There is the kind of view as virtual by default because the query that the view is based on will be executed from the scratch each time when the view is accessed. The query

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many research questions, such as MV maintenance, including incremental update and maintaining strategies, using MV to answer queries and optimization in different fields, in traditional ones such as data warehouse, data streaming, web and semantic web, distributed system and concern future 1. Introduction Materialized views (MV) are special tables where the query execution results are stored, which can be used to answer other queries that appear later. MV is critical and raises

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