ORACLE FAQs :

1. WHAT IS DATA OR INFORMATION?

Ans: The Matter that we feed into the Computer is called Data or Information.



2. WHAT IS DATABASE?

Ans: The Collection of Interrelated Data is called Data Base.



3. WHAT IS A DATABASE MANAGEMENT SYSTEM (DBMS) PACKAGE?

Ans: The Collection of Interrelated Data and some Programs to access the Data is Called Data Base Management System (DBMS).



4. WHEN CAN WE SAY A DBMS PACKAGE AS RDBMS?

Ans: For a system to Qualify as RELATIONAL DATABASE MANAGEMENT system, it must use its RELATIONAL facilities to MANAGE the DATABASE.



5. WHAT IS ORDBMS?

Ans: Object (oriented) Relational Data Base Management System is one that can store data, the relationship of the data, and the behavior of the data (i.e., the way it interacts with other data).



6. NAME SOME CODD'S RULES.

Ans: Dr. E.F. Codd presented 12 rules that a database must obey if it is to be considered truly relational. Out those, some are as follows

a) The rules stem from a single rule- the ‘zero rule’: For a system to Qualify as RELATIONAL DATABASE MANAGEMENT system, it must use its RELATIONAL facilities to MANAGE the DATABASE.

b) Information Rule: Tabular Representation of Information.

c) Guaranteed Access Rule: Uniqueness of tuples for guaranteed accessibility.

d) Missing Information Rule: Systematic representation of missing information as NULL values.

e) Comprehensive Data Sub-Language Rule: QL to support Data definition, View definition, Data manipulation, Integrity, Authorization and Security.





7. WHAT ARE HIERARCHICAL, NETWORK, AND RELATIONAL DATABASE MODELS?

Ans: a) Hierarchical Model: The Hierarchical Model was introduced in the Information Management System (IMS) developed by IBM in 1968. In this data is organized as a tree structure. Each tree is made of nodes and branches. The nodes of the tree represent the record types and it is a collection of data attributes entity at that point. The topmost node in the structure is called the root. Nodes succeeding lower levels are called children.



b) Network Model: The Network Model, also called as the CODSYL database structure, is an improvement over the Hierarchical mode, in this model concept of parent and child is expanded to have multiple parent-child relationships, i.e. any child can be subordinate to many different parents (or nodes). Data is represented by collection of records, and relationships among data are represented by links. A link is an association between precisely two records. Many-to-many relationships can exists between the parent and child.



c) Relational Model: The Relational Database Model eliminates the need for explicit parent-child relationships. In RDBMS, data is organized in two-dimensional tables consisting of relational, i.e. no pointers are maintained between tables.



8. WHAT IS DATA MODELING?

Ans: Data Modeling describes relationship between the data objects. The relationships between the collections of data in a system may be graphically represented using data modeling.



9. DEFINE ENTITY, ATTRIBUTE AND RELATIONSHIP.

Ans: Entity: An Entity is a thing, which can be easily identified. An entity is any object, place, person, concept or activity about which an enterprise records data.

Attribute: An attribute is the property of a given entity.

Relationship: Relationship is an association among entities.





10. WHAT IS ER-MODELING?

Ans: The E-R modeling technique is the Top Down Approach. Entity relationship is technique for analysis and logical modeling of a system’s data requirements. It is the most widely used and has gained acceptance as the ideal database design. It uses three basic units: entities, their attributes and the relationship that exists between the entities. It uses a graphical notation for representing these.



11. WHAT IS NORMALIZATION?

Ans: Normalization is a step-by-step decomposition of complex records into simple records.



12. WHAT ARE VARIOUS NORMAL FORMS OF DATA?

Ans: The First Normal Form 1NF,

The Second Normal Form 2NF,

The Third Normal Form 3NF,

The Boyce and Codd Normal Form BC NF.



13. WHAT IS DENORMALIZATION?

Ans: The intentional introduction of redundancy to a table to improve performance is called DENORMALIZATION.



14. WHAT ARE 1-TIER, 2-TIER, 3-TIER OR N-TIER DATABASE ARCHITECTURES?

Ans: 1-Tier Database Architecture is based on single system, which acts as both server and client.

2-Tier Architecture is based on one server and client.

3-Tier Architecture is based on one server and client out that on client act as a remote system.

N-Tier Architecture is based on N no. Of servers and N no. Of clients.



15. WHAT ARE A TABLE, COLUMN, AND RECORD?

Ans: Table: A Table is a database object that holds your data. It is made up of many columns. Each of these columns has a data type associated with it.



Column: A column, referred to as an attribute, is similar to a field in the file system.



Record: A row, usually referred to as tuple, is similar to record in the file system.



16. WHAT IS DIFFERENCE BETWEEN A PROCEDURAL LANGUAGE AND A NON-PROCEDURAL LANGUAGE?

Ans:

Procedural Language NON-Procedural Language

A program in this implements a step-by-step algorithm to solve the problem. It contains what to do but not how to do



17.WHAT TYPE OF LANGUAGE "SQL" IS?

Ans: SQL is a Non-procedural, 4th generation Language,/ which concerts what to do rather than how to do any process.



18. CLASSIFICATION OF SQL COMMANDS?

Ans:

DDL (Data Definition Language) DML (Data Manipulating Language) DCL (Data Control Language) DTL(Data Transaction Language)

Create Alter Drop Select Insert Update Delete Rollback Commit Grant Revoke





19. WHAT IS DIFFERENCE BETWEEN DDL AND DML COMMANDS?

Ans: For DDL commands autocommit is ON implicitly whereas For DML commands autocommit is to be turned ON explicitly.



20. WHAT IS DIFFERENCE BETWEEN A TRANSACTION AND A QUERY?

Ans: A Transaction is unit of some commands where as Query is a single line request for the information from the database.



21. WHAT IS DIFFERENCE BETWEEN TRUNCATE AND DELETE COMMANDS?

Ans: Truncate Command will delete all the records where as Delete Command will delete specified or all the records depending only on the condition given.



22. WHAT IS DIFFERENCE BETWEEN UPDATE AND ALTER COMMANDS?

Ans: Alter command is used to modify the database objects where as the Update command is used to modify the values of a data base objects.



23. WHAT ARE COMMANDS OF TCL CATEGORY?

Ans: Grant and Revoke are the two commands belong to the TCL Category.



24. WHICH IS AN EFFICIENT COMMAND - TRUNCATE OR DELETE? WHY?

Ans: Delete is the efficient command because using this command we can delete only those records that are not really required.



25. WHAT ARE RULES FOR NAMING A TABLE OR COLUMN?

Ans: 1) Names must be from 1 to 30 bytes long.

2) Names cannot contain quotation marks.

3) Names are not case sensitive.

4) A name must begin with an alphabetic character from your database character set and the characters $ and #. But these characters are discouraged.

5) A name cannot be ORACLE reserved word.

6) A name must be unique across its namespace. Objects in the name space must have different names.

7) A name can be enclosed in double quotes.



26. HOW MANY COLUMNS CAN A TABLE HAVE?

Ans: A Table can have 1000 columns.





27. WHAT ARE DIFFERENT DATATYPES SUPPORTED BY SQL?

Ans: Char (size), Nchar (size), Varchar2 (size), Nvarchar2 (size) data types for character values,

Number (precision, scale), Number, Number (n), Float, Float (binary precision) data types for numerical values,

Date data type for date values,

Long, Raw (size), Long Raw, Clob, Blob, Nclob, Bfile for large objects.













28. WHAT IS DIFFERENCE BETWEEN LONG AND LOB DATATYPES?

Ans:



LOB LONG

1) The maximum size is 4GB. 2) LOBs (except NCLOB) can be attributes of an object type. 3) LOBs support random access to data. 4) Multiple LOB columns per table or LOB attributes in an object type. 1) The maximum size is 2GB. 2) LONGs cannot. 3) LONGs support only sequential access. 4) Only one LONG column was allowed in a table



29. WHAT IS DIFFERENCE BETWEEN CHAR AND VARCHAR2 DATATYPES?

Ans: Varchar2 is similar to Char but can store variable no. Of characters and while querying the table varchar2 trims the extra spaces from the column and fetches the rows that exactly match the criteria.



30. HOW MUCH MEMORY IS ALLOCATED FOR DATE DATATYPE? WHAT IS DEFAULT DATE FORMAT IN ORACLE?

Ans: For Date data type oracle allocates 7 bytes Memory.

Default Date Format is: DD-MON-YY.



31. WHAT IS RANGE FOR EACH DATATYPE OF SQL?

Ans:

Datatype Range

Char Varchar2 Number Float LONG, RAW, LONGRAW Large Objects (LOB’s) 2000 bytes 4000 bytes Precision 1 to 38 Scale -84 to 127 Precision 38 decimals Or 122 binary precision 2 GB 4GB









32. HOW TO RENAME A COLUMN?

Ans: We can’t rename a Column of a table directly. So we follow the following steps.

To Rename a Column:

a) Alter the table specifying new column name to be given and data type.

b) Then copy the values in the column to be renamed into new column.

c) drop the old column.



33. HOW TO DECREASE SIZE OR CHANGE DATATYPE OF A COLUMN?

Ans: To Decrease the size of a Data type of a column

i. Truncate the table first.

ii. Alter the table column whose size is to be decreased using the same name and data type but new size.



34. WHAT IS A CONSTRAINT? WHAT ARE ITS VARIOUS LEVELS?

Ans: Constraint: Constraints are representators of the column to enforce data entity and consistency.There r two levels

1)Column-level constraints 2)Table-level constraints.





35. LIST OUT ALL THE CONSTRAINTS SUPPORTED BY SQL.

Ans: Not Null, Unique, Check, Primary Key and Foreign Key or Referential Integrity.



36. WHAT IS DIFFERENCE BETWEEN UNIQUE+NOT NULL AND PRIMARY KEY?

Ans: Unique and Not Null is a combination of two Constraints that can be present any number of times in a table and can’t be a referential key to any column of an another table where as Primary Key is single Constraint that can be only once for table and can be a referential key to a column of another table becoming a referential integrity.



37. WHAT IS A COMPOSITE PRIMARY KEY?

Ans: A Primary key created on combination of columns is called Composite Primary Key.









38. WHAT IS A CANDIDATE COLUMN? HOW MANY CANDIDATE COLUMNS CAN BE POSSIBLE PER COMPOSITE PRIMARY KEY?

Ans:



39. HOW TO DEFINE A NULL VALUE?

Ans: A NULL value is something which is unavailable, it is neither zero nor a space and any mathematical calculation with NULL is always NULL.



40. WHAT IS NULL? A CONSTRAINT OR DEFAULT VALUE?

Ans: It is a default value.



41. WHAT IS DEFAULT VALUE FOR EVERY COLUMN OF A TABLE?

Ans: NULL.



42. WHAT IS CREATED IMPLICITLY FOR EVERY UNIQUE AND PRIMARY KEY COLUMNS?

Ans: Index.



43. WHAT ARE LIMITATIONS OF CHECK CONSTRAINT?

Ans: In this we can't specify Pseudo Columns like sysdate etc.



44. WHAT IS DIFFERENCE BETWEEN REFERENCES AND FOREIGN KEY CONSTRAINT?

Ans: References is used as column level key word where as foreign key is used as table level constraint.





45. WHAT IS "ON DELETE CASCADE"?

Ans: when this key word is included in the definition of a child table then whenever the records from the parent table is deleted automatically the respective values in the child table will be deleted.



46. WHAT IS PARENT-CHILD OR MASTER-DETAIL RELATIONSHIP?

Ans: A table which references a column of another table(using

References)is called as a child table(detail table) and a table which is being referred is called Parent (Master) Table .





47. HOW TO DROP A PARENT TABLE WHEN IT’S CHILD TABLE EXISTS?

Ans: Using "on delete cascade".



48. IS ORACLE CASE SENSITIVE?

Ans: NO



49. HOW ORACLE IDENTIFIES EACH RECORD OF TABLE UNIQUELY?

Ans: By Creating indexes and reference IDs.



50. WHAT IS A PSEUDO-COLUMN? NAME SOME PSEUDO-COLUMNS OF ORACLE?

Ans: Columns that are not created explicitly by the user and can be used explicitly in queries are called Pseudo-Columns.

Ex:currval,nextval,sysdate….



51. WHAT FOR "ORDER BY" CLAUSE FOR A QUERY?

Ans: To arrange the query result in a specified order(ascending,descending) by default it takes ascending order.



52. WHAT IS "GROUP BY" QUERIES?

Ans: To group the query results based on condition.



53. NAME SOME AGGREGATE FUNCTIONS OF SQL?

Ans: AVG, MAX, SUM, MIN,COUNT.



54. WHAT IS DIFFERENCE BETWEEN COUNT (), COUNT (*) FUNCTIONS?

Ans: Count () will count the specified column whereas count (*) will count total no. of rows in a table.



55. WHAT FOR ROLLUP AND CUBE OPERATORS ARE?

Ans: To get subtotals and grand total of values of a column.



56. WHAT IS A SUB-QUERY?

Ans: A query within a query is called a sub query where the result of inner query will be used by the outer query.



57. WHAT ARE SQL OPERATORS?

Ans: Value (), Ref () is SQL operator.









58. EXPLAIN "ANY","SOME","ALL","EXISTS" OPERATORS?

Ans: Any: The Any (or it’s synonym SOME) operator computes the lowest value from the set and compares a value to each returned by a sub query.

All: ALL compares a value to every value returned by SQL.

Exists: This operator produces a BOOLWAN results. If a sub query produces any result then it evaluates it to TRUE else it evaluates it to FALSE.



59. WHAT IS A CORRELATED SUB QUERY, HOW IT IS DIFFERENT FROM A NORMAL SUB QUERY?

Ans: A correlated subquery is a nested subquery, which is executed once for each ‘Candidate row’ by the main query, which on execution uses a value from a column in the outer query. In normal sub query the result of inner query is dynamically substituted in the condition of the outer query where as in a correlated subquery, the column value used in inner query refers to the column value present in the outer query forming a correlated subquery.



60. WHAT IS A JOIN - TYPES OF JOINS?

Ans: A join is used to combine two or more tables logically to get query results.



There are four types of Joins namely

EQUI Join

NON-EQUI Join

SELF Join

OUTER Join.



61. WHAT ARE MINIMUM REQUIREMENTS FOR AN EQUI-JOIN?

Ans: There shold be atleast one common column between the joining tables.



62. WHAT IS DIFFERENCE BETWEEN LEFT, RIGHT OUTER JOIN?

Ans:If there r any values in one table that do not have corresponding values in the other,in an equi join that row will not be selected.Such rows can be forcefully selected by using outer join symbol(+) on either of the sides(left or right) based on the requirement.









63. WHAT IS DIFFERENCE BETWEEN EQUI AND SELF JOINS?

Ans: SELF JOIN is made within the table whereas

EQUI JOIN is made between different tables having common column.



64. WHAT ARE "SET" OPERATORS?

Ans: UNION, INTERSECT or MINUS is called SET OPERATORS.



65. WHAT IS DIFFERENCE BETWEEN "UNION" AND "UNION ALL"

OPERATORS?

Ans: UNION will return the values distinctly whereas UNION ALL will return even duplicate values.



66. NAME SOME NUMBER, CHARACTER, DATE, CONVERSION, OTHER

FUNCTIONS.

Ans: Number Functions:

Round (m, [n]),

Trunc (m, [n]),

Power (m, n),

Sqrt,

Abs (m),

Ceil (m),

Floor (m),

Mod (m, n)

Character Functions:

Chr (x)

Concert (string1, string2)

Lower (string)

Upper (string)

Substr (string, from_str, to_str)

ASCII (string)

Length (string)

Initcap (string).

Date Functions:

sysdate

Months between (d1, d2)

To_char (d, format)

Last day (d)

Next_day (d, day).

Conversion Functions:

To_char

To_date

To_number









67. WHAT IS DIFFERENCE BETWEEN MAX () AND GREATEST () FUNCTIONS?

Ans: MAX is an aggregate function which takes only one column name of a table as parameter whereas Greatest is a general function which can take any number of values and column names from dual and table respectively.



68. WHAT FOR NVL () FUNCTION IS?

Ans: NVL Function helps in substituting a value in place of a NULL.



69. WHAT FOR DECODE () FUNCTION IS?

Ans: It is substitutes value basis and it actually does an 'if-then-else' test.



70. WHAT IS DIFFERENCE BETWEEN TRANSLATE () AND REPLACE ()

FUNCTIONS?

Ans: Translate() is a superset of functionality provided by Replace().



71. WHAT IS DIFFERENCE BETWEEN SUBSTR () AND INSTR () FUNCTIONS?

Ans: Substr() will return the specified part of a string whereas

Instr() return the position of the specified part of the string.



72. WHAT IS A JULIAN DAY NUMBER?

Ans: It will return count of the no. Of days between January 1, 4712 BC and the given date.







73. HOW TO DISPLAY TIME FROM A DATE DATA?

Ans: By using time format as 'hh [hh24]: mi: ss' in to_char() function.



74. HOW TO INSERT DATE AND TIME INTO A DATE COLUMN?

Ans: By using format 'dd-mon-yy hh [hh24]: mi: ss' in to_date() function.



75. WHAT IS DIFFERENCE BETWEEN TO_DATE () AND TO_CHAR () CONVERSION FUNCTIONS?

Ans: To_date converts character date to date format whereas

To_char function converts date or numerical values to characters.



76. WHAT IS A VIEW? HOW IT IS DIFFERENT FROM A TABLE?

Ans: View is database object, which exists logically but contains no physical data and manipulates the base table. View is saved as a select statement in the database and contains no physical data whereas Table exists physically.



77. WHAT IS DIFFERENCE BETWEEN SIMPLE AND COMPLEX VIEWS?

Ans: Simple views can be modified whereas Complex views(created based on more than one table) cannot be modified.



78. WHAT IS AN INLINE VIEW?

Ans: Inline view is basically a subquery with an alias that u can use like a view inside a SQL statement. It is not a schema object like SQL-object.



79. HOW TO UPDATE A COMPLEX VIEW?

Ans: Using 'INSTEAD OF' TRIGGERS Complex views can be

Updated.

80. WHAT FOR "WITH CHECK OPTION" FOR A VIEW?

Ans: "WITH CHECK OPTION" clause specifies that inserts and updates r performed through the view r not allowed to create rows which the view cannot select and therefore allows integrity constraints and data validation checks to be enforced on data being inserted or updated.



81. WHAT IS AN INDEX? ADVANTAGE OF AN INDEX

Ans: An Index is a database object used n Oracle to provide quick access to rows in a table. An Index increases the performance of the database.



82. WHAT IS A SEQUENCE? PSEUDO-COLUMNS ASSOCIATED WITH SEQUENCE?

Ans: Sequence is a Database Object used to generate unique integers

to use as primary keys. Nextval, Currval are the Pseudo Columns associated with the sequence.



**83. WHAT IS A CLUSTER? WHEN TO USE A CLUSTER? HOW TO DROP A CLUSTER WHEN CLUSTERED TABLE EXISTS?

Ans: Cluster and Indexes are transparent to the user. Clustering is a method of storing tables that are intimately related and are often joined together into the same area on the disk. When cluster table exists then to drop cluster we have to drop the table first then only cluster is to be dropped.



84. WHAT IS A SNAPSHOT OR MATERIALIZED VIEW?

Ans: Materialized views can be used to replicate data. Earlier the data was replicated through CREATE SNAPSHOT command. Now CREATE MATERIALIZED VIEW can be used as synonym for CREATE SNAPSHOT. Query performance is improved using the materialized view as these views pre calculate expensive joins and aggregate operations on the table.





85. WHAT IS A SYNONYM?

Ans: A Synonym is a database object that allows you to create alternate names for Oracle tables and views. It is an alias for a table, view, snapshot, sequence, procedure, function or package.



86. WHAT IS DIFFERENCE BETWEEN PRIVATE AND PUBLIC SYNONYM?

Ans: Only the user or table owner can reference Private synonym whereas any user can reference the Public synonym.



87. WHAT IS DIFFERENCE BETWEEN "SQL" AND "SQL*PLUS" COMMANDS?

Ans: SQL commands are stored in the buffer whereas SQL*PLUS are not.



**88. NAME SOME SQL*PLUS COMMANDS?

Ans: DESC [CRIBE], START, GET, SAVE, / are SQL*PLUS COMMANDS.



89. WHAT ARE "SQL*PLUS REPORTING" COMMANDS?

Ans: SPOOL file-name, SPOOL OUT, TTITLE, BTITLE, BREAK ON, COMPUTE OF [break] ON etc are SQL*PLUS REPORTING COMMANDS.



90. WHAT ARE SYSTEM AND OBJECT PRIVILEGES?

Ans: Connect and Resource etc are System Privileges.