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.
EditExplanation
- 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
Explanation
- 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.