Sql Interview Question and Answers

71. What is UNIQUE KEY constraint?
  A UNIQUE constraint enforces the uniqueness of the values in a set of columns, so no duplicate values are entered. The unique key constraints are used to enforce entity integrity as the primary key constraints.
 
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72. What is NOT NULL Constraint?
  A NOT NULL constraint enforces that the column will not accept null values. The not null constraints are used to enforce domain integrity, as the check constraints.
 
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73. What is meant by query optimization?
  The phase that identifies an efficient execution plan for evaluating a query that has the least estimated cost is referred to as query optimization.
 
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74. What is meant by embedded SQL?
  They are SQL statements that are embedded with in application program and are prepared during the program preparation process before the program is executed.
 
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75. What is File Manager?
  It is a program module, which manages the allocation of space on disk storage and data structure used to represent information stored on a disk.
 
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