Sql Interview Question and Answers

96. What is the difference between TRUNCATE and DELETE commands?
  TRUNCATE is a DDL command whereas DELETE is a DML command. Hence DELETE operation can be rolled back, but TRUNCATE operation cannot be rolled back. WHERE clause can be used with DELETE and not with TRUNCATE.
 
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97. Describe the three levels of data abstraction?
 
    There are three levels of abstraction :
  • Physical level :
    The lowest level of abstraction describes how data are stored.
  • Logical level:
    The next higher level of abstraction, describes what data are stored in database and what relationship among those data.
  • View level:
    The highest level of abstraction describes only part of entire database.
 
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98. How to copy the tables, schema and views from one SQL server to another?
  Microsoft SQL Server 2000 Data Transformation Services (DTS) is a set of graphical tools and programmable objects that lets user extract, transform, and consolidate data from disparate sources into single or multiple destinations.
 
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99. What is the difference between static and dynamic SQL?
  Static SQL is hard-coded in a program when the programmer knows the statements to be executed.
Dynamic SQL the program must dynamically allocate memory to receive the query results.
 
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100. What does COMMIT do?
  A Commit makes permanent the changes resulting from all SQL statements in the transaction. The changes made by the SQL statements of a transaction become visible to other user sessions transactions that start only after transaction is committed.
 
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