Technical Interview Questions and Answers :: Accenture
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Physical level
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A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table. In other words, there is no stored file that directly represents the view instead a definition of the view is stored in data dictionary.
Growth and restructuring of base tables are not reflected in views. Thus the view can insulate users from the effects of restructuring and growth in the database. Hence accounts for logical data independence.
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A collection of conceptual tools for describing data, data relationships data semantics and constraints.
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No Discussion on this question yet!
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Primary key cannot have null value whereas unique key can have null
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It is a special language used to manipulate the Data. Data Manipulation Language (DML), which is used to select, insert, update, and delete data in the objects defined using DDL.
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The PRIMARY KEY is the column(s) used to uniquely identify each row of a table.
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A FOREIGN KEY is one or more columns whose values are based on the PRIMARY or CANDITATE KEY values from the database.
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A UNIQUE KEY is one or more columns that must be unique for each row of the table.
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The UNIQUE KEY column restricts entry of duplicate values but entry of NULL value is allowed. In case of PRIMARY KEY columns entry of duplicate as well as