Sql Interview Question and Answers

106. What are the purpose of Normalisation?
 

  • Minimize redundancy in data.
  • Remove insert, delete and update anamoly during the database activities.
  • Reduce the need to reorganize data it is modified or enhanced.
  • Normalisation reduces a complex user view to a set of small and stable subgroups of fields or relations.
 
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107. What is RAID?
  RAID, an acronym for Redundant Array of Independent Disks (sometimes incorrectly referred to as Redundant Array of Inexpensive Disks), is a technology that provides increased storage functions and reliability through redundancy.
 
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108. What is database replication?
  Replication is the process of copying / moving data between databases on the same or different servers.
 
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109. What are ACID properties?
 

  • Atomicity
  • Consistency
  • Isolation
  • Durability
 
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110. What is diffrence between Co-related sub query and nested sub query?
  Correlated subquery runs once for each row selected by the outer query. It contains a reference to a value from the row selected by the outer query.

Nested subquery runs only once for the entire nesting (outer) query. It does not contain any reference to the outer query row.
 
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