DBMS - Interview Questions and Answers

  1. What is a SQL view? Briefly explain the use of views.
    A SQL view is a virtual table built from other tables or views. Views are used to (1) hide columns or rows, (2) show the results of computed columns, (3) hide complicated SQL syntax, (4) layer built-in functions, (5) provide a level of indirection between application programs and tables, (6) assign different sets of processing permissions to tables, and (7) to assign different sets of triggers to the same table.
  2. Explain the "paradigm mismatch" between SQL and application programming languages.
    SQL statements return a set of rows, while an application program works on one row at a time. To resolve this mismatch the results of SQL statements are processed as pseudofiles, using a cursor or pointer to specify which row is being processed.
  3. Name four applications for triggers.
    (1) providing default values, (2) enforcing data constraints, (3) updating views and (4) enforcing referential integrity
  4. What are stored procedures, and how do they differ from triggers?
    A stored procedure is a program that is stored within the database and is compiled when used. They can receive input parameters and they can return results. Unlike triggers, their scope is database-wide; they can be used by any process that has permission to use the database stored procedure.
  5. What are the advantages of using stored procedures?
    The advantages of stored procedures are (1) greater security, (2) decreased network traffic, (3) the fact that SQL can be optimized and (4) code sharing which leads to less work, standardized processing, and specialization among developers.
  6. Why is database redesign necessary?
    Database redesign is necessary for two reasons. First, redesign is necessary both to fix mistakes made during the initial database design. Second, redesign is necessary to adapt the database to changes in system requirements. Such changes are common because information systems and organizations do not just influence each other they create each other. Thus, new information systems cause changes in systems requirements.

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