Question 18 Following Statements Data Warehouses Correct 1 Column Stores Useful Data Wareh Q29138861

QUESTION 18 Which of the following statements about data warehouses is NOT correct? 1. Column stores can be useful in data warehouses. SQL update performance is more important than SQL aggregate queries in data warehouses, since the data is very large. O Data warehouses typically use a multidimensional data model. C A data warehouse tends to contain data integrated from various sources. QUESTION 19 Consider this query: select* from Temps T1, Temps T2 where Tl.time T2.time and T1.temp <>T2.temp Which of the following statements is correct? CRelations T1 and T2 may not have the same schema. 1. If Temps.temp is a primary key, this query always returns empty results. If and only if there are duplicate tuples in Temps, this query returns nothing as result. This query will return nothing if and only if no two tuples have different temp values but the same time value QUESTION 20 Which of the following statements regarding indexes and views is NOT correct? 1. When a database is shut down and then is restarted, we must create the views again, but not the indexes, because index data is stored on disk, but not the views. We cannot select from the views if we dont create them again. C For any SQL query that involves a view in it, there must be an equivalent SQL query that always returns the same result, but does not use the view. Unlike indexes, a view by default does not have any data maintenance cost for INSERT, UPDATE, and DELETE statements. Unlike views, we typically do not use indexes for access control

QUESTION 18 Which of the following statements about data warehouses is NOT correct? 1. Column stores can be useful in data warehouses. SQL update performance is more important than SQL aggregate queries in data warehouses, since the data is very large. O Data warehouses typically use a multidimensional data model. C A data warehouse tends to contain data integrated from various sources. QUESTION 19 Consider this query: select* from Temps T1, Temps T2 where Tl.time T2.time and T1.temp T2.temp Which of the following statements is correct? CRelations T1 and T2 may not have the same schema. 1. If Temps.temp is a primary key, this query always returns empty results. If and only if there are duplicate tuples in Temps, this query returns nothing as result. This query will return nothing if and only if no two tuples have different temp values but the same time value QUESTION 20 Which of the following statements regarding indexes and views is NOT correct? 1. When a database is shut down and then is restarted, we must create the views again, but not the indexes, because index data is stored on disk, but not the views. We cannot select from the views if we don’t create them again. C For any SQL query that involves a view in it, there must be an equivalent SQL query that always returns the same result, but does not use the view. Unlike indexes, a view by default does not have any data maintenance cost for INSERT, UPDATE, and DELETE statements. Unlike views, we typically do not use indexes for access control Show transcribed image text QUESTION 18 Which of the following statements about data warehouses is NOT correct? 1. Column stores can be useful in data warehouses. SQL update performance is more important than SQL aggregate queries in data warehouses, since the data is very large. O Data warehouses typically use a multidimensional data model. C A data warehouse tends to contain data integrated from various sources. QUESTION 19 Consider this query: select* from Temps T1, Temps T2 where Tl.time T2.time and T1.temp T2.temp Which of the following statements is correct? CRelations T1 and T2 may not have the same schema. 1. If Temps.temp is a primary key, this query always returns empty results. If and only if there are duplicate tuples in Temps, this query returns nothing as result. This query will return nothing if and only if no two tuples have different temp values but the same time value QUESTION 20 Which of the following statements regarding indexes and views is NOT correct? 1. When a database is shut down and then is restarted, we must create the views again, but not the indexes, because index data is stored on disk, but not the views. We cannot select from the views if we don’t create them again. C For any SQL query that involves a view in it, there must be an equivalent SQL query that always returns the same result, but does not use the view. Unlike indexes, a view by default does not have any data maintenance cost for INSERT, UPDATE, and DELETE statements. Unlike views, we typically do not use indexes for access control

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