12. Do View contain Data ? Views do not contain or store data. 13. Can a View based on another View ? Yes. 14. What are the advantages of Views ? Provide an additional level of table security, by restricting access to a predetermined set of rows and columns of a table. Hide data complexity. Simplify commands for the user. Present the data in a different perpecetive from that of the base table. Store complex queries. 15. What is a Sequence ? A sequence generates a serial list of unique numbers for numerical columns of a database's tables. 16. What is a Synonym ? A synonym is an alias for a table, view, sequence or program unit. 17. What are the type of Synonyms? There are two types of Synonyms Private and Public. 18. What is a Private Synonyms ? A Private Synonyms can be accessed only by the owner. 19. What is a Public Synonyms ? A Public synonyms can be accessed by any user on the database. 20. What are synonyms used for ? Synonyms are used to : Mask the real name and owner of an object. Provide public access to an object Provide location transparency for tables,views or program units of a remote database. Simplify the SQL statements for database users. 21. What is an Index ? An Index is an optional structure associated with a table to have direct access to rows,which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table. 22. How are Indexes Update ?
Indexes are automatically maintained and used by ORACLE. Changes to table data are automatically incorporated into all relevant indexes.
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