Oracle Interview Questions

Oracle Sample Questions : Oracle Interview Questions

1.     What is a transaction ?

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

2.     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.

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

Answer: Public synonyms

4.     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.

5.     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.

6.     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'

7.     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; 

8.     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 codeinto 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

9.     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;

     10. What are the various types of queries ?

Answer: The types of queries are:

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

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.

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

Answer: Yes.

13.                        Can you have two stored functions with the same name ?

Answer: Yes.

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

Answer: No.

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

Answer: IN, OUT AND INOUT.

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.

17.                        Can functions be overloaded ?

Answer: Yes.

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

Answer: No.

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

20.                        Why Create or Replace and not Drop and recreate procedures ?

Answer: So that Grants are not dropped.

21.                        Can you pass parameters in packages ? How ?

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

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

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.

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.

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

Answer: One.

26.                        Can views be specified in a trigger statement ?

Answer: No

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

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.

29. What are mutating triggers ?

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

30. What are constraining triggers ?

Answer: A trigger giving an Insert/Updat e on a table having referential integrity constraint on the triggering table.