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PL/SQL INTERVIEW QUESTION & ANSWERS

Databases
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56. What is the Subquery?
  A subquery is a query (usually enclosed by parentheses) that appears within another SQL data manipulation statement. The statement acts upon the single value or set of values returned by the subquery.
  Posted by Hema Kondalarao. (May 13, 2013)
 

Normal sub query works as:
The inner query or the sub query returns a value, this value will be used by the outer query upon the main query.
Where as in correlated sub query:
The information from the outer query select statement participates as a condition in the inner query select statement.
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57. What is correlated subquery?
  While a subquery is evaluated only once for each table, a correlated subquery is evaluated once for each row.
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58. What is an PL/SQL Procedures?
  A procedure is a subprogram that performs a specific action. You write procedures using the SQL CREATE PROCEDURE statement. You specify the name of the procedure, its parameters, its local variables, and the BEGIN-END block that contains its code and handles any exceptions.
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59. What is Database Triggers?
  A database trigger is a stored subprogram associated with a database table, view, or event. The trigger can be called once, when some event occurs, or many times, once for each row affected by an INSERT, UPDATE, or DELETE statement. The trigger can be called after the event, to record it or take some followup action. Or, the trigger can be called before the event to prevent erroneous operations or fix new data so that it conforms to business rules.
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60. What are the types of PL/SQL Triggers?
 
    There are two types of triggers based on the which level it is triggered.
  • Row level trigger : An event is triggered for each row upated, inserted or deleted.
  • Statement level trigger : An event is triggered for each sql statement executed.
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