Sql Interview Question and Answers

36. What is a tuple?
  A tuple is an instance of data within a relational database.
 
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37. 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. After it is prepared, the statement itself does not change(although values of host variables specified within the statement might change).
 
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38. What is Functional Dependency?
  A Functional dependency is denoted by X Y between two sets of attributes X and Y that are subsets of R specifies a constraint on the possible tuple that can form a relation state r of R. The constraint is for any two tuples t1 and t2 in r if t1[X] = t2[X] then they have t1[Y] = t2[Y]. This means the value of X component of a tuple uniquely determines the value of component Y.
 
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39. What are the different phases of transaction?
 
    The different phases of transaction are
  • Analysis phase
  • Redo Phase
  • Undo phase
 
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40. What the difference between UNION and UNIONALL?
  Union will remove the duplicate rows from the result set while Union all does’nt.
 
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