3i Infotech Papers: Sample Questions 633 - 634 of 1245

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Question number: 633

» Database » Oracle

Essay Question▾

Describe in Detail

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

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 number: 634

» Database » MySQL

Essay Question▾

Describe in Detail

What is the use of CASCADE CONSTRAINTS?

Explanation

Define cascading constraints.

Define Cascading Constraints.

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.