3i Infotech Placement: Sample Questions 885 - 886 of 1245

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Question 885

Describe in Detail Essay▾

Name the three major set of files on disk that compose a database in Oracle.

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Explanation

  • Three major sets of files on disk that compose a database.
    • Database files
    • Control files
    • Redo logs
  • The most important of these are the database files where the actual data resides.
  • The control files and the redo logs support the functioning of the architecture itself.
  • All three sets of files must be present, open, and available to Oracle for any data on the database to be useable.
  • Without these files, you cannot access the database, and the database administrator might have to recover some or all of the database using a backup, if there is one.

Question 886

Describe in Detail Essay▾

What is the use of CASCADE CONSTRAINTS?

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Explanation

Define Cascading Constraints
  • When we used the DROP command, a parent table can be dropped even when a child table exists.
  • CASCADE CONSTRAINTS drops referential integrity constraints that refer to primary and unique keys defined on the dropped column.
  • For example:
  • Parent table has branch details

    CREATE TABLE br (bno number constraint mypk1 primary key,

    bname varchar2 (60) )

  • Child table contains student information corresponding to branch

    CREATE TABLE st (sno number constraints mypk2 primary key,

    sname varchar2 (100) ,

    bno number,

  • Constraints pmfk1 foreign key (bno) references br (bno) on delete cascade
  • Cascade constraint is enforced- thus when any records from br table are deleted- corresponding (with reference to bno) records in the st are also deleted.