Oracle Interview Question and Answers

21. What is a database instance?
  A database instance is a set of memory structure and background processes that access a set of database files. The processes can be shared by all of the users.
22. What are parameters?
  Parameters provide a simple mechanism for defining and setting the valuesof inputs that are required by a form at startup.Form parameters are variables of type char,number,date that you define at design time.
23. What are the different file extensions that are created by oracle reports?
  Rep file and Rdf file.
24. What are clusters?
  Clusters are groups of one or more tables physically stores together to share common columns and are often used together.
25. What is difference between SUBSTR and INSTR?
  INSTR function search string for sub-string and returns an integer indicating the position of the character in string that is the first character of this occurrence.SUBSTR function return a portion of string, beginning at character position, substring_length characters long.SUBSTR calculates lengths using characters as defined by the input character set.
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