ORACLE SQL Interview Practical Questions with Queries With Answers Part 4

51) What is SET?

SET command changes the system variables affecting the report environment.

52) What is SPOOL?

SPOOL command creates a print file of the report.

53) What is a JOIN?

JOIN is the form of SELECT command that combines info from two or more tables.

Types of Joins are Simple (Equijoin & Non-Equijoin), Outer & Self join.

Equijoin returns rows from two or more tables joined together based upon a equality condition in the WHERE clause.

Non-Equijoin returns rows from two or more tables based upon a relationship other than the equality condition in the WHERE clause.

Outer Join combines two or more tables returning those rows from one table that have no direct match in the other table.

Self Join joins a table to itself as though it were two separate tables.

54) What is Union?

Union is the product of two or more tables.

55) What is Intersect?

Intersect is the product of two tables listing only the matching rows.

56) What is Minus?

Minus is the product of two tables listing only the non-matching rows.

57)What is Correlated Subquery?

Correlated Subquery is a subquery that is evaluated once for each row processed by the parent statement. Parent statement can be Select, Update or Delete. Use CRSQ to answer multipart questions whose answer depends on the value in each row processed by parent statement.

58) What is Multiple columns?

Multiple columns can be returned from a Nested Subquery.

59) What is Sequences?

Sequences are used for generating sequence numbers without any overhead of locking. Drawback is that after generating a sequence number if the transaction is rolled back, then that sequence number is lost. 

Sequence is a database object used to generate unique sequential integer values.

60) What is Synonyms?

Synonyms is the alias name for table, views, sequences & procedures and are created for reasons of Security and Convenience.Two levels are Public - created by DBA & accessible to all the users. Private - Accessible to creator only. Advantages are referencing without specifying the owner and Flexibility to customize a more meaningful naming convention.

61) What is Data types?

Max. columns in a table is 255. Max. Char size is 255, Long is 64K & Number is 38 digits.

Cannot Query on a long column.

Char, Varchar2 Max. size is 2000 & default is 1 byte.

Number(p,s) p is precision range 1 to 38, s is scale -84 to 127.

Long Character data of variable length upto 2GB.

Date Range from Jan 4712 BC to Dec 4712 AD.

Raw Stores Binary data (Graphics Image & Digitized Sound). Max. is 255 bytes.

Mslabel Binary format of an OS label. Used primarily with Trusted Oracle.

62) What is Transaction?

Transaction is defined as all changes made to the database between successive commits.

63) What is Commit?

Commit is an event that attempts to make data in the database identical to the data in the form. It involves writing or posting data to the database and committing data to the database. Forms check the validity of the data in fields and records during a commit. Validity check are uniqueness, consistency and db restrictions.

64) What is Posting?

Posting is an event that writes Inserts, Updates & Deletes in the forms to the database but not committing these transactions to the database.

65) What is Savepoint?

Savepoint is a point within a particular transaction to which you may rollback without rolling back the entire transaction.

66) What is Set Transaction?

Set Transaction is to establish properties for the current transaction.

67) What is Locking?

Locking are mechanisms intended to prevent destructive interaction between users accessing data. Locks are used to achieve.

68) What is SQL Deadlock?

Deadlock is a unique situation in a multi user system that causes two or more users to wait indefinitely for a locked resource. First user needs a resource locked by the second user and the second user needs a resource locked by the first user. To avoid dead locks, avoid using exclusive table lock and if using, use it in the same sequence and use Commit frequently to release locks

.

69) Give the structure of the procedure ?

PROCEDURE name (parameter list.....)

is

local variable declarations

BEGIN

Executable statements.

Exception.

exception handlers

end;

basically procedure has three

parts

1.variable declaretion(optional)

2.body(mandetory)

3.Exception(optional)

suppose ex

CREATE OR REPLACEPROCEDURE emp_pro( p_id IN employees.employee_id%TYPE)

IS

v_name employees.last_name%TYPE;

v_mail employees.email%TYPE;

BEGIN

SELECT last_name,email INTO v_name,v_mail FROM employees

WHERE employee_id:=p_id;

DBMS_OUTPUT.PUT_LINE('NAME:'||v_name ||'MAILID:'||v_mail);

END;

70) What is Mutating SQL Table?

Mutating Table is a table that is currently being modified by an Insert, Update or Delete statement. Constraining Table is a table that a triggering statement might need to read either directly for a SQL statement or indirectly for a declarative Referential Integrity constraints. Pseudo Columns behaves like a column in a table but are not actually stored in the table. E.g. Currval, Nextval, Rowid, Rownum, Level etc.

71) What is SQL*Loader?

SQL*Loader is a product for moving data in external files into tables in an Oracle database. To load data from external files into an Oracle database, two types of input must be provided to SQL*Loader : the data itself and the control file. The control file describes the data to be loaded. It describes the Names and format of the data files, Specifications for loading data and the Data to be loaded (optional). Invoking the loader sqlload username/password controlfilename <options>.

72) What are the return values of functions SQLCODE and SQLERRM ?

SQLCODE returns the latest code of the error that has occurred.

SQLERRM returns the relevant error message of the SQLCODE.

SQLCODE returns the latest code of the error that has occured.

SQLERRM returns relevant massege

of the error code

73) The most important DDL statements in SQL are?

CREATE TABLE - creates a new database table

ALTER TABLE - alters (changes) a database table

DROP TABLE - deletes a database table

CREATE INDEX - creates an index (search key)

DROP INDEX - deletes an index

74) Operators used in SELECT statements are?

= Equal

<> or != Not equal

> Greater than

< Less than

>= Greater than or equal

<= Less than or equal

BETWEEN Between an inclusive range

LIKE Search for a pattern

75) SELECT statements in SQL?

SELECT column_name(s) FROM table_name

SELECT DISTINCT column_name(s) FROM table_name

SELECT column FROM table WHERE column operator value

SELECT column FROM table WHERE column LIKE pattern

SELECT column,SUM(column) FROM table GROUP BY column

SELECT column,SUM(column) FROM table GROUP BY column HAVING SUM(column) condition value

Note that single quotes around text values and numeric values should not be enclosed in quotes. Double quotes may be acceptable in some databases.

76) What are the PL/SQL Statements used in cursor processing ?

DECLARE CURSOR cursor name, OPEN cursor name, FETCH cursor name INTO or Record types, CLOSE cursor name.

77) The SELECT INTO Statement is most often used to create backup copies of tables or for archiving records?

SELECT column_name(s) INTO newtable [IN externaldatabase] FROM source

SELECT column_name(s) INTO newtable [IN externaldatabase] FROM source WHERE column_name operator value.

78) The INSERT INTO Statements in SQL?

INSERT INTO table_name VALUES (value1, value2,....)

INSERT INTO table_name (column1, column2,...) VALUES (value1, value2,....)

79) The Update Statement in SQL.

UPDATE table_name SET column_name = new_value WHERE column_name = some_value

80) What is the Delete Statements in SQL?

Delete statement in SQL is used to delete partial/all data.

Especially delete statement is useful in case of partial delete depending upon our criterias otherwise use TRUNCATE to delete whole data from table.

When delete command fires then:

1) Triggers will fire (If created on that table)

2) This will not auto commit changes made So there is one chance to rollback.

3) If u delete whole data then HWM (Highest Water Mark) will not change which gets changed in case of Truncate.

81) How to sort the rows in SQL?

SELECT column1, column2, ... FROM table_name ORDER BY columnX, columnY, ..

SELECT column1, column2, ... FROM table_name ORDER BY columnX DESC

SELECT column1, column2, ... FROM table_name ORDER BY columnX DESC, columnY ASC

82) The IN operator may be used if you know the exact value you want to return for at least one of the columns.

SELECT column_name FROM table_name WHERE column_name IN (value1,value2,..)

                 *******Thank you for reading and All the best**************

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