Sql Interview Question and Answers

76. Define Constraints?
 
    Constraints is a rule or restriction concerning a piece of data that is enforced at the data level.
    A Constraint clause can constrain a single column or group of columns in a table.
    There are five types of Constraint namely
  • Null / Not Null
  • Primary Key
  • Unique
  • Check or Validation
  • Foreign Key or References Key
 
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77. What are types of sub-queries?
 
  • Single-row subquery, where the subquery returns only one row.
  • Multiple-row subquery, where the subquery returns multiple rows.
  • Multiple column subquery, where the subquery returns multiple columns.
 
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78. What is SQL Profiler?
  SQL Profiler is a graphical tool that allows system administrators to monitor events in an instance of Microsoft SQL Server. You can capture and save data about each event to a file or SQL Server table to analyze later.
 
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79. Define Clusters?
  Clustering is a method of storing tables that are intimately related and often joined together into the same area on disk.
A cluster contains one or more tables, which have one or more column in common among them.
 
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80. Define Indexes?
  Index is a general term for an Oracle/SQL features used to primarily to speed execution and imposes uniqueness upon certain data.
The most important of an index is to ensure uniqueness of rows and help in speedy retrieval of data.
 
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