Oracle Concepts and Architecture Interview Questions and
Answers
1.
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What
are the components of Physical database structure of Oracle Database?
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ORACLE
database is comprised of three types of files. One or more Data files, two
are more Redo Log files, and one or more Control files.
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2.
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What
are the components of Logical database structure of ORACLE database?
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Tablespaces
and the Database's Schema Objects.
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3.
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What
is a Tablespace?
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A
database is divided into Logical Storage Unit called tablespaces. A
tablespace is used to grouped related logical structures together.
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4.
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What
is SYSTEM tablespace and When is it Created?
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Every
ORACLE database contains a tablespace named SYSTEM, which is automatically
created when the database is created. The SYSTEM tablespace always contains
the data dictionary tables for the entire database.
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5.
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Explain
the relationship among Database, Tablespace and Data file.
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Each
databases logically divided into one or more tablespaces One or more data
files are explicitly created for each tablespace.
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6.
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What
is schema?
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A
schema is collection of database objects of a User.
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7.
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What
are Schema Objects ?
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Schema
objects are the logical structures that directly refer to the database's
data. Schema objects include tables,views,sequences,synonyms, indexes,
clusters, database triggers, procedures, functions packages and database
links.
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8.
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Can
objects of the same Schema reside in different tablespaces.?
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Yes.
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9.
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Can
a Tablespace hold objects from different Schemes ?
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Yes.
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10.
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what
is Table ?
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A
table is the basic unit of data storage in an ORACLE database. The tables of
a database hold all of the user accessible data. Table data is stored in rows
and columns.
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11.
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What
is a View ?
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A
view is a virtual table. Every view has a Query attached to it. (The Query is
a SELECT statement that identifies the columns and rows of the table(s) the
view uses.)
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12.
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Do
View contain Data ?
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Views
do not contain or store data.
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13.
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Can
a View based on another View ?
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Yes.
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14.
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What
are the advantages of Views ?
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•Provide
an additional level of table security, by restricting access to a predetermined
set of rows and columns of a table.
•Hide data complexity. •Simplify commands for the user. •Present the data in a different perpecetive from that of the base table. •Store complex queries. |
15.
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What
is a Sequence ?
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A
sequence generates a serial list of unique numbers for numerical columns of a
database's tables.
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16.
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What
is a Synonym ?
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A
synonym is an alias for a table, view,sequence or program unit.
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17.
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What
are the type of Synonyms ?
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There
are two types of Synonyms Private and Public.
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18.
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What
is a Private Synonyms ?
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A
Private Synonyms can be accessed only by the owner.
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19.
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What
is a Public Synonyms ?
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A
Public synonyms can be accessed by any user on the database.
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20.
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What
are synonyms used for ?
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Synonyms
are used to : Mask the real name and owner of an object.
Provide public access to an object Provide location transparency for tables,views or program units of a remote database. Simplify the SQL statements for database users. |
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21.
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What
is an Index ?
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An
Index is an optional structure associated with a table to have direct access
to rows,which can be created to increase the performance of data retrieval.
Index can be created on one or more columns of a table.
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22.
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How
are Indexes Update ?
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Indexes
are automatically maintained and used by ORACLE. Changes to table data are
automatically incorporated into all relevant indexes.
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23.
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What
are Clusters ?
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Clusters
are groups of one or more tables physically stores together to share common
columns and are often used together.
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24.
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What
is cluster Key ?
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The
related columns of the tables in a cluster is called the Cluster Key.
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25.
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What
is Index Cluster ?
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A
Cluster with an index on the Cluster Key.
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26.
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What
is Hash Cluster ?
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A
row is stored in a hash cluster based on the result of applying a hash
function to the row's cluster key value. All rows with the same hash key
value are stores together on disk.
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27.
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When
can Hash Cluster used ?
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Hash
clusters are better choice when a table is often queried with equality
queries. For such queries the specified cluster key value is hashed. The
resulting hash key value points directly to the area on disk that stores the
specified rows.
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28.
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What
is Database Link ?
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A
database link is a named object that describes a "path" from one
database to another.
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29.
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What
are the types of Database Links?
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Private
Database Link, Public Database Link & Network Database Link.
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30.
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What
is Private Database Link?
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Private
database link is created on behalf of a specific user. A private database
link can be used only when the owner of the link specifies a global object
name in a SQL statement or in the definition of the owner's views or
procedures.
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31.
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What
is Public Database Link?
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Public
database link is created for the special user group PUBLIC. A public database
link can be used when any user in the associated database specifies a global
object name in a SQL statement or object definition.
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32.
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What
is Network Database link?
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Network
database link is created and managed by a network domain service. A network
database link can be used when any user of any database in the network
specifies a global object name in a SQL statement or object definition.
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33.
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What
is Data Block?
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ORACLE
database's data is stored in data blocks. One data block corresponds to a
specific number of bytes of physical database space on disk.
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34.
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How
to define Data Block size?
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A
data block size is specified for each ORACLE database when the database is
created. A database users and allocated free database space in ORACLE
datablocks. Block size is specified in INIT.ORA file and cann't be changed
latter.
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35.
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What
is Row Chaining?
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In
Circumstances, all of the data for a row in a table may not be able to fit in
the same data block. When this occurs, the data for the row is stored in a
chain of data block (one or more) reserved for that segment.
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36.
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What
is an Extent?
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An
Extent is a specific number of contiguous data blocks, obtained in a single
allocation, used to store a specific type of information.
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37.
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What
is a Segment?
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A
segment is a set of extents allocated for a certain logical structure.
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38.
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What
are the different types of Segments?
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Data
Segment, Index Segment, Rollback Segment and Temporary Segment.
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39.
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What
is a Data Segment?
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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.
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40.
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What
is an Index Segment?
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Each
Index has an Index segment that stores all of its data.
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41.
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What
is Rollback Segment?
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A
Database contains one or more Rollback Segments to temporarily store
"undo" information.
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42.
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What
are the uses of Rollback Segment?
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Rollback
Segments are used:
To generate read-consistent database information during database recovery to rollback uncommitted transactions for users. |
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43.
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What
is a Temporary Segment?
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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.
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44.
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What
is a Data File?
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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.
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45.
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What
are the Characteristics of Data Files?
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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. |
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46.
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What
is a Redo Log?
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The
set of Redo Log files for a database is collectively known as the database's
redo log.
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47.
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What
is the function of Redo Log?
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The
Primary function of the redo log is to record all changes made to data.
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48.
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What
is the use of Redo Log Information?
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The
Information in a redo log file is used only to recover the database from a
system or media failure the prevents database data from being written to a
database's data files.
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49.
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What
does a Control file Contain?
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A
Control file records the physical structure of the database. It contains the
following information.
•Database Name •Names and locations of a database's files and redolog files. •Time stamp of database creation. |
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50.
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What
is the use of Control File?
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When
an instance of an ORACLE database is started, its control file is used to
identify the database and redo log files that must be opened for database
operation to proceed. It is also used in database recovery.
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51.
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What
is a Data Dictionary?
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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. |
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52.
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What
is an Integrity Constrains?
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An
integrity constraint is a declarative way to define a business rule for a
column of a table.
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53.
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Can
an Integrity Constraint be enforced on a table if some existing table data
does not satisfy the constraint?
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No.
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54.
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Describe
the different type of Integrity Constraints supported by ORACLE?
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•NOT
NULL Constraint - Disallows NULLs 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. |
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55.
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What
is difference between UNIQUE constraint and PRIMARY KEY constraint?
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A
column defined as UNIQUE can contain NULLs while a column defined as PRIMARY
KEY can't contain Nulls.
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56.
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Describe
Referential Integrity?
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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.
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57.
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What
are the Referential actions supported by FOREIGN KEY integrity constraint?
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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. |
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58.
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What
is self-referential integrity constraint?
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If
a foreign key reference a parent key of the same table is called
self-referential integrity constraint.
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59.
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What
are the Limitations of a CHECK Constraint?
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The
condition must be a Boolean expression evaluated using the values in the row
being inserted or updated and can't contain subqueries, sequence, the
SYSDATE,UID,USER or USERENV SQL functions, or the pseudocolumns LEVEL or
ROWNUM.
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60.
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What
is the maximum number of CHECK constraints that can be defined on a column?
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No
Limit.
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