1.
What is an Extent?
An
Extent is a specific number of contiguous data blocks, obtained in a single
allocation, and used to store a specific type of information.
2.
What is a Segment?
A
segment is a set of extents allocated for a certain logical structure.
3.
What is the different type of Segments?
Data
Segment, Index Segment, Rollback Segment and Temporary Segment.
4.
What is a Data Segment?
Each
Non-clustered table has a data segment. All of the table's data is stored in
the extents of its data segment. Each cluster has a data segment. The data of
every table in the cluster is stored in the cluster's data segment.
5.
What is an Index Segment?
Each
Index has an Index segment that stores all of its data.
6.
What is Rollback Segment?
A
Database contains one or more Rollback Segments to temporarily store
"undo" information.
7.
What are the uses of Rollback Segment?
Rollback
Segments are used:
To
generate read-consistent database information during database recovery to
rollback uncommitted transactions for users.
8.
What is a Temporary Segment?
Temporary
segments are created by ORACLE when a SQL statement needs a temporary work area
to complete execution. When the statement finishes execution, the temporary
segment extents are released to the system for future use.
9.
What is a Data File?
Every
ORACLE database has one or more physical data files. A database's data files
contain all the database data. The data of logical database structures such as
tables and indexes is physically stored in the data files allocated for a
database.
10.
What are the Characteristics of Data Files?
A
data file can be associated with only one database. Once created a data file
can't change size.
One
or more data files form a logical unit of database storage called a tablespace.
11.
What is a Data Dictionary?
The
data dictionary of an ORACLE database is a set of tables and views that are
used as a read-only reference about the database.
It
stores information about both the logical and physical structure of the
database, the valid users of an ORACLE database, integrity constraints defined
for tables in the database and space allocated for a schema object and how much
of it is being used.
12.
What is an Integrity Constrains?
An
integrity constraint is a declarative way to define a business rule for a
column of a table.
13.
Can an Integrity Constraint be enforced on a table if some existing table data
does not satisfy the constraint?
No.
14.
Describe the different type of Integrity Constraints supported by ORACLE?
NOT
NULL Constraint - Disallows NULL's in a table's column.
UNIQUE
Constraint - Disallows duplicate values in a column or set of columns.
PRIMARY
KEY Constraint - Disallows duplicate values and NULLs in a column or set of
columns.
FOREIGN
KEY Constrain - Require each value in a column or set of columns match a value
in a related table's UNIQUE or PRIMARY KEY.
CHECK
Constraint - Disallows values that do not satisfy the logical expression of the
constraint.
15.
What is difference between UNIQUE constraint and PRIMARY KEY constraint?
A
column defined as UNIQUE can contain NULLs while a column defined as PRIMARY
KEY can't contain Nulls.
16.
Describe Referential Integrity?
A
rule defined on a column (or set of columns) in one table that allows the
insert or update of a row only if the value for the column or set of columns
(the dependent value) matches a value in a column of a related table (the
referenced value). It also specifies the type of data manipulation allowed on
referenced data and the action to be performed on dependent data as a result of
any action on referenced data.
17.
What are the Referential actions supported by FOREIGN KEY integrity constraint?
UPDATE
and DELETE Restrict - A referential integrity rule that disallows the update or
deletion of referenced data.
DELETE
Cascade - When a referenced row is deleted all associated dependent rows are
deleted.
18.
What is self-referential integrity constraint?
If
a foreign key reference a parent key of the same table is called
self-referential integrity constraint.
19.
What are the Limitations of a CHECK Constraint?
The
condition must be a Boolean expression evaluated using the values in the row
being inserted or updated and can't contain sub-queries, sequence, the
SYSDATE, UID, USER or USERENV SQL functions, or the pseudo columns LEVEL or
ROWNUM.
20.
What is the maximum number of CHECK constraints that can be defined on a column?
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