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Oracle Sample Questions : Oracle Interview Questions

1. What are the various types of queries ?

   Answer: The types of queries are:

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

2. What is a transaction ?

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

3. 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.

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

   Answer: Public synonyms

5. 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.

6. 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.

7. 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'

8. 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;
   

9. 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

10. 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;