RDBMS Topic 4 Adv. SQL, MSBTE Questions and Answers ( 12 Marks)

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1 2017 RDBMS Topic 4 Adv. SQL, MSBTE Questions and Answers ( 12 Marks)

2 2016 Q. What is view? Definition of view: 2 marks) Ans : View: A view is a logical extract of a physical relation i.e. it is derived from any base relation. OR View: Views are virtual relations mainly used for security purpose, and can be provided on request by a particular user. Q. Consider following schema. ( 4 Marks) Employee (empname, empid, dob, salary, job) Create a view on employee having attribute (empname, empid, dob, salary, job) where salary is greater than 20,000. Ans: Create view EMPVIEW as select empname, empid, dob, salary, job from employee where salary>20000; OR CREATE VIEW EMPVIEW AS SELECT * FROM EMPLOYEE WHERE SALARY >20000; Q. What are views? Give its syntax and explain its advantages. (Views - 2 marks; Syntax - 1 mark; Advantages (Any two) - 1 mark)

3 Views are created for security reasons. Instead of coping same table multiple times for different requirements, views can be created. View is a logical copy of physical table. It doesn t exist physically. With the help of view, we can give restricted access to users. When view is used, underlying table is invisible, thus increasing security. Views can be used to see, insert, update and delete data from base table. Syntax for creating view:- Create [OR Replace][Force /Noforce] view <viewname>[alias name.] As subquery [with CHECK OPTION[CONSTRAINT]] [with READ ONLY]; Advantages of Views: Views restrict access to the data because the view can display selective columns from the table. Views can be used to make simple queries to retrieve the results of complicated queries. For example, views can be used to query information from multiple tables without the user knowing how to write a join statement. Views provide data independence for adhoc users and application programs. One view can be used to retrieve data from several tables. Views provide groups of users to access to data according to their particular criteria. Thus implements security and authorization Explain views with example. (Explanation of view with syntax 3 Marks, Example - 1 Mark)

4 Views are created for security reasons. Instead of coping same table multiple times for different requirements, views can be created. View is a logical copy of physical table. It doesn t exist physically. With the help of view, we can give restricted access to users. When view is used,underlying table is invisible, thus increasing security. Views can be used to see, insert, update and delete data from base table. Syntax for creating view:- Create [OR Replace][Force /Noforce] view <viewname>[alias name.] As subquery [with CHECK OPTION[CONSTRAINT]] [with READ ONLY]; Example : Create view emp_info as select Emp_no, Emp_name from Employee where salary>12000; To describe content of view Select * from emp_info; To describe structure of view describe emp_info; Q. How to create view? (Syntax OR Example of view - 2 Marks) Ans: Syntax for creating view. Create view <viewname> as select <query>; OR Example : Create viewemp_info as select Emp_no, Emp_name from Employee;

5 2014 Q. Write the syntax for creating a view. (Syntax- 2 Marks) Ans: Syntax for creating view. Create view <viewname> as select <query> 2016 Q. What are sequence? Why it is used? Create sequence for STUDENT table. (Definition - 1 mark; Use - 1 mark; creating valid sequence example/pattern - 2 marks) Ans: Definition: A sequence refers to a database object that is capable of generating unique and sequential integer values. Use: 1. It saves a time by reducing application code. 2. It is used to generate unique sequential integers. 3. It is used to create an auto number fields. 4. Sequence can be use for many tables/relations Sequence for student table: Create sequence student_seq increment by 1 start with 1 maxvalue 60 nocycle; 2015 Q Explain sequences with example. (Definition of sequence - 1 Mark, syntax 2 Marks, Example - 1 Mark) Ans: Definition A sequence refers to a database object that is capable of generating unique and sequential integer values.

6 Syntax: Create sequence <seq_name> [increment by num] [start with num] [maxvalue num] [minvaluenum][cycle/nocycle][cache num/nocache]; Where, Increment by num: Used to specify the interval between sequence numbers. Start with num: States the first sequence numbers that needs to be generated. Minvalue num: This is used to state the minimum value of the sequence. Maxvalue num :It states the maximum value generated by sequence. Cycle: Cycle indicates that the sequence will be continued for generating the values from thestarting after reaching either its maximum value or minimum value. Cache: The cache option is used to pre-allocates a set of sequence numbers and keep these numbers in the memory so that they can be accessed. No Cache: This states that there is no pre-allocation for the values of sequence. Example: Create sequence student_seq increment by 1 start with 1 maxvalue 60 nocycle; Q. What is sequence? What are the various operations with respect to sequences? (Sequence explanation 2 Marks, any two operations 2 Marks) Ans: Sequence : exists a column which can uniquely identify the record from a table. For that purpose, that column has to be a primary key which can never contain duplicate or null value.

7 minimized by creating sequence for automatic entry of certain values which are in sequence. be inserted into a table. The value generated can have maximum of 38 digits. numeric values. Operations allowed on sequence: 1) Create a sequence : Create sequence < sequence name > [incremented by <integer value> start with <integer value>maxvalue<integer value>/nomaxvalue minvalue<integer value>/nominvalue cycle/ nocycle] cache<integer value>/nocache order/noorder INCREMENT BY:Specifies the interval between sequence number. It can be any positive or negative value but not zero. If this clause is omitted the default value is 1. MINIVALUE: Specifies the sequence minimum value. NOMINVALUE: Specifies the maximum value of 1 for an ascending sequence and (10)^26 for a descending sequence. MAXVALUE: Specifies the maximum value that a sequence can generate.

8 NOMAXVALUE: Specifies a maximum of 10^27 for an ascending sequence or -1 for a descending sequence is the sequence minimum value(1) and for a descending sequence, it is the maximum value(-1). CYCLE: Specifies that the sequence continues to generate repeat values after reaching either its maximum. NOCYCLE: Specifies that a sequence cannot generate more values after reaching the maximum value. Example Create sequence addr_sqe increment by 1 start with 1 minivalue 1 maxvalue 999 cycle; 2) Referncing a sequence Once a sequence is created SQL can be used to view the values held in its cache. To simply view sequence value use a SELECT sentence as describe below. SELECT<SequenceName>.NextVal FROM DUAL; Every time nextval reference a sequence its output is automatically increment from the old values to the values to the new value ready for use. INSERT INTO ADDR_DTLS(ADDR_NO,CODE_NO,ADDR_TYPE,ADDR1,ADDR2,CITY,STATE,PINCODE)VALUES(ADDR_SEQ.NextVal, B5, B, Vertex Plaza,Shop 4,, Western Express Highway,Dahisar(East),, Mumbai, ); To reference the current value of a sequence: SELECT<SequenceName>.CURRVAL FROM DUAL; 3) Altering a sequence A sequence once created can be altered. This is achieved by using the ALTER SEQUENCE statement.

9 SYNTAX: ALTER SEQUENCE<SequenceName> [Increment by <IntegerValue> Maximum<IntegerValue>/NOMAXVALUE MINVALUE<IntegerValue>/NOMINVALUE CYCLE/NOCYCLE CACHE<IntegerValue>/NOCACHE ORDER/NOORDER] Change the cache value of the sequence ADDR_SEQ to 30 and interval between two numbers as 2. Example - ALTER SEQUENCEADDR_SEQ INCREMENT BY 2 CACHE 30; 4) Dropping a Sequence The DROP SEQUENCE command is used to remove the sequence from database. Syntax: DROP SEQUENCE<SequenceName>; 2014 What are sequences? Write syntax for creating sequence. (Explanation -2 Marks, Syntax-2 Marks) Ans: Sequence: It is database object that generate/produce integer values in sequential order. It automatically generates primary key and unique key values. It may be ascending or descending order. It can be used for multiple tables. Sequence numbers are stored and generated independently of tables. Syntax: Create sequence <seq_name> Start with [initial value]

10 Increment by [value] Minvalue [minimum value] Maxvalue [maximum value] [cycle/nocycle] [{cache value / No cache}] [{order / No order}]; 2017 Q. Define index. ( 2 Marks) Ans: Index: An index is a schema object that can speed up the retrieval of rows by using pointer. An Index provides direct and fast access to rows in a table. Q. Describe unique index and composite index with example.(4 marks) Ans: Unique Index: Unique indexes are used not only for performance, but also for data integrity. An unique index does not allow any duplicate values to be inserted into the table. The basic syntax is as follows: CREATE UNIQUE INDEX index_name on table_name (column_name); Example: CREATE UNIQUE INDEX ename_idx on emp (ename); Composite Index: A composite index is an index created on two or more columns of a table. The basic syntax is as follows: CREATE INDEX index_name on table_name (column1, column2);

11 Example: CREATE INDEX en_idx on emp (ename,job); 2016 Q. What is index? Explain types of index. (Index Definition - 2 marks; Any Two Types - 1 mark each) Ans: Index: An index is a schema object that can speed up the retrieval of rows by using pointer. An index provides direct and fast access to rows in a table. Indexes are created explicitly Or automatically. Indexes are used to speed up searches/queries. Types of Index: Simple index (Single column): An index created on single column of a table is called a Simple Index. Unique indexes are used not only for performance, but also for data integrity. A unique index does not allow any duplicate values to be inserted into the table. Composite (concatenated): Indexes that contain two or more columns from the same table which are useful for enforcing uniqueness in a table column where there s no single column that can uniquely identify a row. Q. Explain the following terms with syntax and example: ( 4Marks) a) Simple Index b) Composite Index c) Unique Index. a) Simple Index: A simple index is one that is created based on only one column of a table.

12 The basic syntax is as follows: CREATE INDEX index_name ON table_name (column_name); Example: CREATE INDEX ename_idx on emp (ename); b) Composite Index: A composite index is an index created on two or more columns of a table. The basic syntax is as follows: CREATE INDEX index_name on table_name (column1, column2); Example: CREATE INDEX en_idx on emp (ename,job); c) Unique Indexes: Unique indexes are used not only for performance, but also for data integrity. A unique index does not allow any duplicate values to be inserted into the table. The basic syntax is as follows: CREATE UNIQUE INDEX index_name on table_name (column_name); Example: CREATE UNIQUE INDEX ename_idx on emp (ename); 2015 Q. Explain the concept of indexing with neat diagram. (Explanation - 3 Marks, Any relevant Diagram - 1 Mark)

13 Ans: Index: An index is a schema object that can speed up the retrieval of rows by using pointer. An index provides direct and fast access to rows in a table. Indexes are created explicitly Or automatically. Indexes are used to speed up searches/queries. Types of Index: Simple index(single column): An index created on single column of a table is called a Simple Index. Unique indexes are used not only for performance, but also for data integrity. A unique index does not allow any duplicate values to be inserted into the table. Composite (concatenated): Indexes that contain two or more columns from the same table which are useful for enforcing uniqueness in a table column where there s no single column that can uniquely identify a row. Q Explain with example simple and composite index. (Simple Index Explanation & Example-2 Marks, Composite Index Explanation &Example- 2 Marks)

14 Ans: Simple index: An index created on single column of a table is called a Simple Index. Syntax: Create index on <tablename><column name>; E.g.: Create index idx on employee (empno); Composite Index:An Index that contain two or more columns from the same table is called as Composite Index. Syntax: Create index on <tablename><column name1, Column name 2>; E.g.: Create index idx on employee (ename, empno); 2014 Q. Describe following terms: i) unique indexes ii) composite indexes. (Each index 2 Marks) i) Unique indexes are used not only for performance, but also for data integrity. A unique index does not allow any duplicate values to be inserted into the table. The basic syntax is as follows: Create unique index index_name on table_name(column_name); The example is as follows: Create unique index index_empno on emp(empno); ii) Composite index is an index on two or more columns of a table. To create a composite index, take into consideration the columns that you may use very frequently in a query's WHERE clause as filter conditions. If there are two or more columns that are frequently used in the WHERE clause as filters, the composite index would be the best choice.

15 The basic syntax is as follows: Create index index_name on table_name(column1,column2); The example is as follows: Create index index_empdept on emp(empno,deptno); 2017 Q. Explain snapshot with example. (4 Marks) Snapshot: It is also known as materialized view. It is a copy of either an entire single table or set of its rows or collection of tables, views or rows using join, grouping and selection criteria. Useful in distributed environment It has two types: Simple snapshot and complex snapshot. Simple snapshot related to single table and complex snapshot related to joined tables. Example : Operations on snapshot: i) Creating Snapshot: Create snapshot command is used to create the snapshot. Syntax:- CREATE SNAPSHOT [schema.] <snapshot name>as subquery; Example:- Create snapshot emp_snapas select * from emp where deptno=6; ii) Altering snapshot: Snapshot can be altered by using ALTER SNAPSHOT command.

16 The only parts ofa snapshot that can be altered are its storage parameters, refresh type and refresh start,and next interval. The select for the snapshot, base tables, and other data related items cannot be changed without dropping and recreating the snapshot. Syntax:- ALTER SNAPSHOT <snapshotname> [[PCTFREE <integer>] [PCTUSED <integer>] [REFRESH [FAST/COMPLETE/FORCE]]; Example:- To change the automatic refresh mode for the emp_data snapshot to fast: ALTER SNAPSHOT emp_data REFRESH FAST; iii) Dropping a snapshot To remove the snapshot DROP SNAPSHOT Command.When snapshot is dropped which a snapshot log had associated with it, only the rows required for maintainingthat snapshot are dropped. Syntax:- Drop snapshot <snapshot name>; Example:- Drop snapshot emp_snap; 2016 What are snapshots? Give its uses. How to create a snapshot? (Definition - 1 mark; any one Use - 1 mark, Syntax/Example - 2 marks) Ans: Snapshots:

17 It is also known as materialized view. It is a copy of either an entire single table or set of its rows or collection of tables, Views or either rows using join, grouping and selection criteria. Uses: Useful in distributed environment. Response time of the queries gets minimized as the client has made a local copy of master table. If the master table gets corrupted, then data can be restored using snapshot. Creating Snapshots: Create snapshot command is used to create the snapshot. Syntax: Create snapshot snapshot_name refresh with rowid as <select query>; Example: Create snapshot emp_snap refresh with rowid as select * from emp; Q. Explain the following terms with syntax and example. (4 Marks) i) Creating snapshot ii) Altering snapshot iii) Dropping a snapshot. i) Creating Snapshot: Create snapshot command is used to create the snapshot. Syntax:- CREATE SNAPSHOT [schema.] <snapshot name> AS subquery;

18 Example:- Create snapshot emp_snap as select * from emp where deptno=6; ii) Altering snapshot Snapshot can be altered by using ALTER SNAPSHOT command. The only parts of a snapshot that can be altered are its storage parameters, refresh type and refresh start, and next interval. The select for the snapshot, base tables, and other data related items cannot be changed without dropping and recreating the snapshot. Syntax:- ALTER SNAPSHOT <snapshotname> [[PCTFREE <integer>] [PCTUSED <integer>] [REFRESH [FAST/COMPLETE/FORCE]]; Example:- To change the automatic refresh mode for the emp_data snapshot to fast: ALTERSNAPSHOT emp_data REFRESH FAST; iii) Dropping a snapshot To remove the snapshot DROP SNAPSHOT Command.When snapshot is dropped which a snapshot log had associated with it, only the rows required for maintaining that snapshot are dropped. Syntax:- Drop snapshot <snapshot name>; Example:- Drop snapshot emp_snap;

19 2015 Explain snapshot with example. (Explanation of snapshot 3 Marks, example 1 Mark) Ans: Snapshot: It is also known as materialized view. It is a copy of either an entire single table or set of its rows or collection of tables, views or rows using join, grouping and selection criteria. Useful in distributed environment It has two types: Simple snapshot and complex snapshot. Simple snapshot related to single table and complex snapshot related to joined tables. Example: Snapshot for emp table: Create snapshot emp_data refresh with rowid as select * from emp; Q. Write a PL/SQL program to create any snapshot. (Creation of snapshot 2 Marks, PL/SQL code 2Marks) [Note: Any other relevant example of PL/SQL code can be considered] Ans: 1) To create a snapshot : Create snapshot emp_snap refresh with rowid as select * from emp; 2) To use snapshot from PL/SQL : declare cnt as number(2):=0; begin

20 Select count(*) into cnt from emp_snap; dbms_output.put_line ( Number of rows from snapshot : cnt); end; 2014 Q. What is snapshot? Write the syntax for creating a snapshot. (Explanation- 2 Marks, Syntax- 2 Marks) Ans: Snapshot: It is also known as materialized view. It is a copy of either an entire single table or set of its rows or collection of tables, Views or either rows using join, grouping and selection criteria. Useful in distributed environment It has two types: Simple snapshot and complex snapshot. Simple snapshot related to single table and complex snapshot related to joined tables. Syntax: Create snapshot snapshot_name Pctfree n Pctused n Tablespace tablespace_name Storage clause Refresh Star with date As select statement; OR Create snapshot snapshot_name As select statement; 2014 Q What are synonyms? Write a syntax for creating a synonym. (Synonym definition -2 Marks, Correct syntax -2 Marks)

21 Ans: A synonym is an alternative name for objects such as tables, views, sequences, stored procedures, and other database objects. You generally use synonyms when you are granting access to an object from another schema and you don't want the users to have to worry about knowing which schema owns the object. Syntax: CREATE [OR REPLACE] [PUBLIC] SYNONYM [schema.] synonym_name FOR [schema.] object_name; OR create synonym synonym_name for object_name; DROP SYNONYM Once a synonym has been created in Oracle, you might at some point need to drop the synonym. Syntax The syntax to drop a synonym in Oracle is: DROP [PUBLIC] SYNONYM [schema.] synonym_name [force]; PUBLIC Allows you to drop a public synonym. If you have specified PUBLIC, then you don't specify a schema. force It will force Oracle to drop the synonym even if it has dependencies. It is probably not a good idea to use force as it can cause invalidation of Oracle objects. Example Let's look at an example of how to drop a synonym in Oracle. For example:

22 DROP PUBLIC SYNONYM suppliers; This DROP statement would drop the synonym called suppliers that we defined earlier.