Set - 10

Question 1 :

Why is a Where clause faster than a group filter or a format trigger?

Answer :

Because, in a where clause the condition is applied during data retrievalthan after retrieving the data.


Question 2 :

Can one selectively load only the records that one need? (for DBA)

Answer :

Look at this example, (01) is the first character, (30:37) are characters 30 to 37:
LOAD DATA
INFILE 'mydata.dat' BADFILE 'mydata.bad' DISCARDFILE 'mydata.dis'
APPEND
INTO TABLE my_selective_table
WHEN (01) <> 'H' and (01) <> 'T' and (30:37) = '19991217'
(
region CONSTANT '31',
service_key POSITION(01:11) INTEGER EXTERNAL,
call_b_no POSITION(12:29) CHAR
)


Question 3 :

Can one skip certain columns while loading data? (for DBA)

Answer :

One cannot use POSTION(x:y) with delimited data. Luckily, from Oracle 8i one can specify FILLER columns. FILLER columns are used to skip columns/fields in the load file, ignoring fields that one does not want. Look at this example: -- One cannot use POSTION(x:y) as it is stream data, there are no positional fields-the next field begins after some delimiter, not in column X. -->
LOAD DATA
TRUNCATE INTO TABLE T1
FIELDS TERMINATED BY ','
( field1,
field2 FILLER,
field3
)


Question 4 :

How does one load multi-line records? (for DBA)

Answer :

One can create one logical record from multiple physical records using one of the following two clauses:
. CONCATENATE: - use when SQL*Loader should combine the same number of physical records together to form one logical record.
. CONTINUEIF - use if a condition indicates that multiple records should be treated as one. Eg. by having a '#' character in column 1.


Question 5 :

How can get SQL*Loader to COMMIT only at the end of the load file? (for DBA)

Answer :

One cannot, but by setting the ROWS= parameter to a large value, committing can be reduced. Make sure you have big rollback segments ready when you use a high value for ROWS=.


Question 6 :

Can one improve the performance of SQL*Loader? (for DBA)

Answer :

A very simple but easily overlooked hint is not to have any indexes and/or constraints (primary key) on your load tables during the load process. This will significantly slow down load times even with ROWS= set to a high value.
Add the following option in the command line: DIRECT=TRUE. This will effectively bypass most of the RDBMS processing. However, there are cases when you can't use direct load. Refer to chapter 8 on Oracle server Utilities manual.
Turn off database logging by specifying the UNRECOVERABLE option. This option can only be used with direct data loads. Run multiple load jobs concurrently.


Question 7 :

How does one use SQL*Loader to load images, sound clips and documents? (for DBA)

Answer :

SQL*Loader can load data from a "primary data file", SDF (Secondary Data file - for loading nested tables and VARRAYs) or LOGFILE. The LOBFILE method provides and easy way to load documents, images and audio clips into BLOB and CLOB columns. Look at this example:
Given the following table:
CREATE TABLE image_table (
image_id NUMBER(5),
file_name VARCHAR2(30),
image_data BLOB);
Control File:
LOAD DATA
INFILE *
INTO TABLE image_table
REPLACE
FIELDS TERMINATED BY ','
(
image_id INTEGER(5),
file_name CHAR(30),
image_data LOBFILE (file_name) TERMINATED BY EOF
)
BEGINDATA
001,image1.gif
002,image2.jpg


Question 8 :

What is the difference between the conventional and direct path loader? (for DBA)

Answer :

The conventional path loader essentially loads the data by using standard INSERT statements. The direct path loader (DIRECT=TRUE) bypasses much of the logic involved with that, and loads directly into the Oracle data files. More information about the restrictions of direct path loading can be obtained from the Utilities Users Guide.


Question 9 :

What are the various types of Exceptions ?

Answer :

User defined and Predefined Exceptions.


Question 10 :

Can we define exceptions twice in same block ?

Answer :

No.


Question 11 :

What is the difference between a procedure and a function ?

Answer :

Functions return a single variable by value whereas procedures do not return any variable by value. Rather they return multiple variables by passing variables by reference through their OUT parameter.


Question 12 :

Can you have two functions with the same name in a PL/SQL block ?

Answer :

Yes.


Question 13 :

Can you have two stored functions with the same name ?

Answer :

Yes.


Question 14 :

Can you call a stored function in the constraint of a table ?

Answer :

No.


Question 15 :

What are the various types of parameter modes in a procedure ?

Answer :

IN, OUT AND INOUT.


Question 16 :

What is Over Loading and what are its restrictions ?

Answer :

OverLoading means an object performing different functions depending upon the no. of parameters or the data type of the parameters passed to it.


Question 17 :

Can functions be overloaded ?

Answer :

Yes.


Question 18 :

Can 2 functions have same name & input parameters but differ only by return datatype ?

Answer :

No.


Question 19 :

What are the constructs of a procedure, function or a package ?

Answer :

The constructs of a procedure, function or a package are :
variables and constants
cursors
exceptions


Question 20 :

Why Create or Replace and not Drop and recreate procedures ?

Answer :

So that Grants are not dropped.


Question 21 :

Can you pass parameters in packages ? How ?

Answer :

Yes. You can pass parameters to procedures or functions in a package.


Question 22 :

What are the parts of a database trigger ?

Answer :

The parts of a trigger are:
A triggering event or statement
A trigger restriction
A trigger action


Question 23 :

What are the various types of database triggers ?

Answer :

There are 12 types of triggers, they are combination of :
Insert, Delete and Update Triggers.
Before and After Triggers.
Row and Statement Triggers.
(3*2*2=12)


Question 24 :

What is the advantage of a stored procedure over a database trigger ?

Answer :

We have control over the firing of a stored procedure but we have no control over the firing of a trigger.


Question 25 :

What is the maximum no. of statements that can be specified in a trigger statement ?

Answer :

One.


Question 26 :

Can views be specified in a trigger statement ?

Answer :

No


Question 27 :

What are the values of :new and :old in Insert/Delete/Update Triggers ?

Answer :

INSERT : new = new value, old = NULL
DELETE : new = NULL, old = old value
UPDATE : new = new value, old = old value


Question 28 :

What are cascading triggers? What is the maximum no of cascading triggers at a time?

Answer :

When a statement in a trigger body causes another trigger to be fired, the triggers are said to be cascading. Max = 32.


Question 29 :

What are mutating triggers ?

Answer :

A trigger giving a SELECT on the table on which the trigger is written.


Question 30 :

What are constraining triggers ?

Answer :

A trigger giving an Insert/Update on a table having referential integrity constraint on the triggering table.


Question 31 :

Describe Oracle database's physical and logical structure ?

Answer :

Physical : Data files, Redo Log files, Control file.
Logical : Tables, Views, Tablespaces, etc.


Question 32 :

Can you increase the size of a tablespace ? How ?

Answer :

Yes, by adding datafiles to it.


Question 33 :

What is the use of Control files ?

Answer :

Contains pointers to locations of various data files, redo log files, etc.


Question 34 :

What is the use of Data Dictionary ?

Answer :

Used by Oracle to store information about various physical and logical Oracle structures e.g. Tables, Tablespaces, datafiles, etc


Question 35 :

What are the advantages of clusters ?

Answer :

Access time reduced for joins.


Question 36 :

What are the disadvantages of clusters ?

Answer :

The time for Insert increases.


Question 37 :

Can Long/Long RAW be clustered ?

Answer :

No.


Question 38 :

Can null keys be entered in cluster index, normal index ?

Answer :

Yes.


Question 39 :

Can Check constraint be used for self referential integrity ? How ?

Answer :

Yes. In the CHECK condition for a column of a table, we can reference some other column of the same table and thus enforce self referential integrity.


Question 40 :

What are the min. extents allocated to a rollback extent ?

Answer :

Two


Question 41 :

What are the states of a rollback segment ? What is the difference between partly available and needs recovery ?

Answer :

The various states of a rollback segment are :
ONLINE, OFFLINE, PARTLY AVAILABLE, NEEDS RECOVERY and INVALID.


Question 42 :

What is the difference between unique key and primary key ?

Answer :

Unique key can be null; Primary key cannot be null.


Question 43 :

An insert statement followed by a create table statement followed by rollback ? Will the rows be inserted ?

Answer :

No.


Question 44 :

an you define multiple savepoints ?

Answer :

Yes.


Question 45 :

Can you Rollback to any savepoint ?

Answer :

Yes.


Question 46 :

What is the maximum no. of columns a table can have ?

Answer :

254.


Question 47 :

What is the significance of the & and && operators in PL SQL ?

Answer :

The & operator means that the PL SQL block requires user input for a variable. The && operator means that the value of this variable should be the same as inputted by the user previously for this same variable. If a transaction is very large, and the rollback segment is not able to hold the rollback information, then will the transaction span across different rollback segments or will it terminate ? It will terminate (Please check ).


Question 48 :

Can you pass a parameter to a cursor ?

Answer :

Explicit cursors can take parameters, as the example below shows. A cursor parameter can appear in a query wherever a constant can appear. CURSOR c1 (median IN NUMBER) IS SELECT job, ename FROM emp WHERE sal > median;


Question 49 :

What are the various types of RollBack Segments ?

Answer :

Public Available to all instances
Private Available to specific instance


Question 50 :

Can you use %RowCount as a parameter to a cursor ?

Answer :

Yes
Is the query below allowed :
Select sal, ename Into x From emp Where ename = 'KING'
(Where x is a record of Number(4) and Char(15))
Yes
Is the assignment given below allowed :
ABC = PQR (Where ABC and PQR are records)
Yes
Is this for loop allowed :
For x in &Start..&End Loop
Yes


Question 51 :

How many rows will the following SQL return :

Answer :

Select * from emp Where rownum < 10;
9 rows


Question 52 :

How many rows will the following SQL return :

Answer :

Select * from emp Where rownum = 10;
No rows


Question 53 :

Which symbol preceeds the path to the table in the remote database ?

Answer :

@


Question 54 :

Are views automatically updated when base tables are updated ?

Answer :

Yes


Question 55 :

Can a trigger written for a view ?

Answer :

No


Question 56 :

If all the values from a cursor have been fetched and another fetch is issued, the output will be : error, last record or first record ?

Answer :

Last Record


Question 57 :

A table has the following data : [[5, Null, 10]]. What will the average function return ?

Answer :

7.5


Question 58 :

Is Sysdate a system variable or a system function?

Answer :

System Function


Question 59 :

Consider a sequence whose currval is 1 and gets incremented by 1 by using the nextval reference we get the next number 2. Suppose at this point we issue an rollback and again issue a nextval. What will the output be ?

Answer :

3


Question 60 :

Definition of relational DataBase by Dr. Codd (IBM)?

Answer :

A Relational Database is a database where all data visible to the user is organized strictly as tables of data values and where all database operations work on these tables.


Question 61 :

What is Multi Threaded Server (MTA) ?

Answer :

In a Single Threaded Architecture (or a dedicated server configuration) the database manager creates a separate process for each database user. But in MTA the database manager can assign multiple users (multiple user processes) to a single dispatcher (server process), a controlling process that queues request for work thus reducing the databases memory requirement and resources.


Question 62 :

Which are initial RDBMS, Hierarchical & N/w database ?

Answer :

RDBMS - R system
Hierarchical - IMS
N/W - DBTG


Question 63 :

What is Functional Dependency

Answer :

Given a relation R, attribute Y of R is functionally dependent on attribute X of R if and only if each X-value has associated with it precisely one -Y value in R


Question 64 :

What is Auditing ?

Answer :

The database has the ability to audit all actions that take place within it.
a) Login attempts, b) Object Accesss, c) Database Action Result of Greatest(1,NULL) or Least(1,NULL) NULL


Question 65 :

While designing in client/server what are the 2 imp. things to be considered ?

Answer :

Network Overhead (traffic), Speed and Load of client server


Question 66 :

When to create indexes ?

Answer :

To be created when table is queried for less than 2% or 4% to 25% of the table rows.


Question 67 :

How can you avoid indexes ?

Answer :

TO make index access path unavailable - Use FULL hint to optimizer for full table scan - Use INDEX or AND-EQUAL hint to optimizer to use one index or set to indexes instead of another. - Use an expression in the Where Clause of the SQL.


Question 68 :

What is the result of the following SQL :

Answer :

Select 1 from dual
UNION
Select 'A' from dual;
Error


Question 69 :

Can database trigger written on synonym of a table and if it can be then what would be the effect if original table is accessed.

Answer :

Yes, database trigger would fire.


Question 70 :

Can you alter synonym of view or view ?

Answer :

No


Question 71 :

Can you create index on view ?

Answer :

No


Question 72 :

What is the difference between a view and a synonym ?

Answer :

Synonym is just a second name of table used for multiple link of database. View can be created with many tables, and with virtual columns and with conditions. But synonym can be on view.


Question 73 :

What is the difference between alias and synonym ?

Answer :

Alias is temporary and used with one query. Synonym is permanent and not used as alias.


Question 74 :

What is the effect of synonym and table name used in same Select statement ?

Answer :

Valid


Question 75 :

What's the length of SQL integer ?

Answer :

32 bit length


Question 76 :

What is the difference between foreign key and reference key ?

Answer :

Foreign key is the key i.e. attribute which refers to another table primary key. Reference key is the primary key of table referred by another table.


Question 77 :

Can dual table be deleted, dropped or altered or updated or inserted ?

Answer :

Yes


Question 78 :

If content of dual is updated to some value computation takes place or not ?

Answer :

Yes


Question 79 :

If any other table same as dual is created would it act similar to dual?

Answer :

Yes


Question 80 :

For which relational operators in where clause, index is not used ?

Answer :

<> , like '% ...' is NOT functions, field +constant, field || ''


Question 81 :

Assume that there are multiple databases running on one machine. How can you switch from one to another ?

Answer :

Changing the ORACLE_SID


Question 82 :

What are the advantages of Oracle ?

Answer :

Portability : Oracle is ported to more platforms than any of its competitors, running on more than 100 hardware platforms and 20 networking protocols.
Market Presence : Oracle is by far the largest RDBMS vendor and spends more on R & D than most of its competitors earn in total revenue. This market clout means that you are unlikely to be left in the lurch by Oracle and there are always lots of third party interfaces available.
Backup and Recovery : Oracle provides industrial strength support for on-line backup and recovery and good software fault tolerence to disk failure. You can also do point-in-time recovery.
Performance : Speed of a 'tuned' Oracle Database and application is quite good, even with large databases. Oracle can manage > 100GB databases.
Multiple database support : Oracle has a superior ability to manage multiple databases within the same transaction using a two-phase commit protocol.


Question 83 :

What is a forward declaration ? What is its use ?

Answer :

PL/SQL requires that you declare an identifier before using it. Therefore, you must declare a subprogram before calling it. This declaration at the start of a subprogram is called forward declaration. A forward declaration consists of a subprogram specification terminated by a semicolon.


Question 84 :

What are actual and formal parameters ?

Answer :

Actual Parameters : Subprograms pass information using parameters. The variables or expressions referenced in the parameter list of a subprogram call are actual parameters. For example, the following procedure call lists two actual parameters named emp_num and amount:
Eg. raise_salary(emp_num, amount);
Formal Parameters : The variables declared in a subprogram specification and referenced in the subprogram body are formal parameters. For example, the following procedure declares two formal parameters named emp_id and increase: Eg. PROCEDURE raise_salary (emp_id INTEGER, increase REAL) IS current_salary REAL;


Question 85 :

What are the types of Notation ?

Answer :

Position, Named, Mixed and Restrictions.


Question 86 :

What all important parameters of the init.ora are supposed to be increased if you want to increase the SGA size ?

Answer :

In our case, db_block_buffers was changed from 60 to 1000 (std values are 60, 550 & 3500) shared_pool_size was changed from 3.5MB to 9MB (std values are 3.5, 5 & 9MB) open_cursors was changed from 200 to 300 (std values are 200 & 300) db_block_size was changed from 2048 (2K) to 4096 (4K) {at the time of database creation}.
The initial SGA was around 4MB when the server RAM was 32MB and The new SGA was around 13MB when the server RAM was increased to 128MB.


Question 87 :

If I have an execute privilege on a procedure in another users schema, can I execute his procedure even though I do not have privileges on the tables within the procedure ?

Answer :

Yes


Question 88 :

What are various types of joins ?

Answer :

Equijoins, Non-equijoins, self join, outer join


Question 89 :

What is a package cursor ?

Answer :

A package cursor is a cursor which you declare in the package specification without an SQL statement. The SQL statement for the cursor is attached dynamically at runtime from calling procedures.


Question 90 :

If you insert a row in a table, then create another table and then say Rollback. In this case will the row be inserted ?

Answer :

Yes. Because Create table is a DDL which commits automatically as soon as it is executed. The DDL commits the transaction even if the create statement fails internally (eg table already exists error) and not syntactically.


Question 91 :

What are the various types of queries ??

Answer :

Normal Queries
Sub Queries
Co-related queries
Nested queries
Compound queries


Question 92 :

What is a transaction ?

Answer :

A transaction is a set of SQL statements between any two COMMIT and ROLLBACK statements.


Question 93 :

What is implicit cursor and how is it used by Oracle ?

Answer :

An implicit cursor is a cursor which is internally created by Oracle. It is created by Oracle for each individual SQL.


Question 94 :

Which of the following is not a schema object : Indexes, tables, public synonyms, triggers and packages ?

Answer :

Public synonyms


Question 95 :

What is PL/SQL?

Answer :

PL/SQL is Oracle's Procedural Language extension to SQL. The language includes object oriented programming techniques such as encapsulation, function overloading, information hiding (all but inheritance), and so, brings state-of-the-art programming to the Oracle database server and a variety of Oracle tools.


Question 96 :

Is there a PL/SQL Engine in SQL*Plus?

Answer :

No. Unlike Oracle Forms, SQL*Plus does not have a PL/SQL engine. Thus, all your PL/SQL are send directly to the database engine for execution. This makes it much more efficient as SQL statements are not stripped off and send to the database individually.


Question 97 :

Is there a limit on the size of a PL/SQL block?

Answer :

Currently, the maximum parsed/compiled size of a PL/SQL block is 64K and the maximum code size is 100K. You can run the following select statement to query the size of an existing package or procedure.
SQL> select * from dba_object_size where name = 'procedure_name'


Question 98 :

Can one read/write files from PL/SQL?

Answer :

Included in Oracle 7.3 is a UTL_FILE package that can read and write files. The directory you intend writing to has to be in your INIT.ORA file (see UTL_FILE_DIR=... parameter). Before Oracle 7.3 the only means of writing a file was to use DBMS_OUTPUT with the SQL*Plus SPOOL command.
DECLARE
fileHandler UTL_FILE.FILE_TYPE;
BEGIN
fileHandler := UTL_FILE.FOPEN('/home/oracle/tmp', 'myoutput','W');
UTL_FILE.PUTF(fileHandler, 'Value of func1 is %sn', func1(1));
UTL_FILE.FCLOSE(fileHandler);
END;


Question 99 :

How can I protect my PL/SQL source code?

Answer :

PL/SQL V2.2, available with Oracle7.2, implements a binary wrapper for PL/SQL programs to protect the source code. This is done via a standalone utility that transforms the PL/SQL source code into portable binary object code (somewhat larger than the original). This way you can distribute software without having to worry about exposing your proprietary algorithms and methods. SQL*Plus and SQL*DBA will still understand and know how to execute such scripts. Just be careful, there is no "decode" command available.
The syntax is:
wrap iname=myscript.sql oname=xxxx.yyy


Question 100 :

Can one use dynamic SQL within PL/SQL? OR Can you use a DDL in a procedure ? How ?

Answer :

From PL/SQL V2.1 one can use the DBMS_SQL package to execute dynamic SQL statements.
Eg: CREATE OR REPLACE PROCEDURE DYNSQL
AS
cur integer;
rc integer;
BEGIN
cur := DBMS_SQL.OPEN_CURSOR;
DBMS_SQL.PARSE(cur,'CREATE TABLE X (Y DATE)', DBMS_SQL.NATIVE);
rc := DBMS_SQL.EXECUTE(cur);
DBMS_SQL.CLOSE_CURSOR(cur);
END;