ORACLE DBA INTERVIEW QUESTIONS AND ANSWERS
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21. What are the conditions to
achieve the normalization?
There are few conditions to
achieve the normalization :
There should be a unique row
identifier.A table should store only data for a single type of entity.A table
should avoid columns which can be null–able.A table should avoid duplication of
data and columns
22. What statement must you
include in your CREATE TRIGGER statement if the trigger definition includes
more than one triggered SQL statement?
BEGIN...END
statement
23. What is INDEX?
Index can speed up
execution and impose UNIQUENESS upon data. You can use an index to gain fast
access to specific information in a database table. An index is a structure
that orders the values of one or more columns in a database table. The index
provides pointers to the data values stored in specified columns of the table,
and then orders those pointers according to the sort order you specify
24 Define BCNF?
BCNF
stands for Boyce-COdd normal form.
A relation is said to be in Boyce-COdd normal form. If it is already in the third normal form and every determinant is a candidate key. It is a stronger version of 3NF.
A relation is said to be in Boyce-COdd normal form. If it is already in the third normal form and every determinant is a candidate key. It is a stronger version of 3NF.
25. What
is a ROWID?
ROWID is
the logical address of a row, and it is unique within the database.
26. What
is the difference between normalization and denormalization?
Normalization data means
eliminating redundant information from a table and organizing the data so that
future changes to the table are easier. Denormalization means allowing
redundancy in a table.
The main benefit of
denormalization is improved performance with simplified data retrieval and
manipulation
27. What is the difference
between table and view?
Table: Stores the data in the
database on the disk drive.Uses a lot of disk space for a large table. The data
belongs to the table.The data in a table is stable and does not change by
itself.
View : Stores the select
statement that defines the view. It has no data of its own.
Uses very little disk space.The
data does not belong to the view. It belongs to the table used in the select
statement that defines the view.The data in a view is dynamic and changes when
the data in the underlying tables is changed
28. What is the difference
between a HAVING CLAUSE and a WHERE CLAUSE?
Having Clause with the GROUP BY
function in a query and WHERE Clause is applied to each row before, they are
part of the GROUP BY function in a query.
29. What can cause a high value for recursive calls? How can this be fixed?
A high value for recursive calls is cause by improper cursor usage, excessive dynamic space management actions, and or excessive statement re-parses. You need to determine the cause and correct it By either relinking applications to hold cursors, use proper space management techniques (proper storage and sizing) or ensure repeat queries are placed in packages for proper reuse.
30. How transferring a table from one schema to another:
There are several possible methods, export-import, CREATE TABLE...
AS SELECT, or COPY.
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