Oracle-Interview-questions

2. You have just had to restore from backup and do not have any control files. How would you go about bringing up this database?
I would create a text based backup control file, stipulating where on disk all the data files where and then issue the recover command with the using backup control file clause.
3. How do you switch from an init.ora file to a spfile?
Issue the create spfile from pfile command.
4. Explain the difference between a data block, an extent and a segment.
A data block is the smallest unit of logical storage for a database object. As objects grow they take chunks of additional storage that are composed of contiguous data blocks. These groupings of contiguous data blocks are called extents. All the extents that an object takes when grouped together are considered the segment of the database object.
5. Give two examples of how you might determine the structure of the table DEPT.
Use the describe command or use the dbms_metadata.get_ddl package.
6. Where would you look for errors from the database engine?
In the alert log.
7. Compare and contrast TRUNCATE and DELETE for a table.
Both the truncate and delete command have the desired outcome of getting rid of all the rows in a table. The difference between the two is that the truncate command is a DDL operation and just moves the high water mark and produces a now rollback. The delete command, on the other hand, is a DML operation, which will produce a rollback and thus take longer to complete.
8. Give the reasoning behind using an index.
Faster access to data blocks in a table.
9. Give the two types of tables involved in producing a star schema and the type of data they hold.
Fact tables and dimension tables. A fact table contains measurements while dimension tables will contain data that will help describe the fact tables.
10. What type of index should you use on a fact table?
A Bitmap index.
11. Give two examples of referential integrity constraints.
A primary key and a foreign key.
12. A table is classified as a parent table and you want to drop and re-create it. How would you do this without affecting the children tables?
Disable the foreign key constraint to the parent, drop the table, re-create the table, enable the foreign key constraint.
13. Explain the difference between ARCHIVELOG mode and NOARCHIVELOG mode and the benefits and disadvantages to each.
ARCHIVELOG mode is a mode that you can put the database in for creating a backup of all transactions that have occurred in the database so that you can recover to any ball in time. NOARCHIVELOG mode is basically the absence of ARCHIVELOG mode and has the disadvantage of not being able to recover to any ball in time. NOARCHIVELOG mode does have the advantage of not having to write transactions to an archive log and thus increases the performance of the database slightly.
14. What command would you use to create a backup control file?
Alter database backup control file to trace.
15. Give the stages of instance startup to a usable state where normal users may access it.
STARTUP NOMOUNT - Instance startup
STARTUP MOUNT - The database is mounted
STARTUP OPEN - The database is opened
16. What column differentiates the V$ views to the GV$ views and how?
The INST_ID column which indicates the instance in a RAC environment the information came from.
17. How would you go about generating an EXPLAIN plan?
Create a plan table with utlxplan.sql.
Use the explain plan set statement_id = 'tst1' into plan_table for a SQL statement
Look at the explain plan with utlxplp.sql or utlxpls.sql
18. How would you go about increasing the buffer cache hit ratio?
Use the buffer cache advisory over a given workload and then query the v$db_cache_advice table. If a change was necessary then I would use the alter system set db_cache_size command.
19. Explain an ORA-01555
You get this error when you get a snapshot too old within rollback. It can usually be solved by increasing the undo retention or increasing the size of rollbacks. You should also look at the logic involved in the application getting the error message.
20. Explain the difference between $ORACLE_HOME and $ORACLE_BASE.
ORACLE_BASE is the root directory for oracle. ORACLE_HOME located beneath ORACLE_BASE is where the oracle products reside.
1. Describe the difference between a procedure, function and anonymous pl/sql block.
Candidate should mention use of DECLARE statement, a function must return a value while a procedure doesn?t have to.

2. What is a mutating table error and how can you get around it?
This happens with triggers. It occurs because the trigger is trying to update a row it is currently using. The usual fix involves either use of views or temporary tables so the database is selecting from one while updating the other.

3. Describe the use of %ROWTYPE and %TYPE in PL/SQL
Expected answer: %ROWTYPE allows you to associate a variable with an entire table row. The %TYPE associates a variable with a single column type.

4. 4What packages (if any) has Oracle provided for use by developers?
Expected answer: Oracle provides the DBMS_ series of packages. There are many which developers should be aware of such as DBMS_SQL, DBMS_PIPE, DBMS_TRANSACTION, DBMS_LOCK, DBMS_ALERT, DBMS_OUTPUT, DBMS_JOB, DBMS_UTILITY, DBMS_DDL, UTL_FILE. If they can mention a few of these and describe how they used them, even better. If they include the SQL routines provided by Oracle, great, but not really what was asked.

5. Describe the use of PL/SQL tables
Expected answer: PL/SQL tables are scalar arrays that can be referenced by a binary integer. They can be used to hold values for use in later queries or calculations. In Oracle 8 they will be able to be of the %ROWTYPE designation, or RECORD.

6. When is a declare statement needed ?
The DECLARE statement is used in PL/SQL anonymous blocks such as with stand alone, non-stored PL/SQL procedures. It must come first in a PL/SQL stand alone file if it is used.

7. In what order should a open/fetch/loop set of commands in a PL/SQL block be implemented if you use the %NOTFOUND cursor variable in the exit when statement? Why?
Expected answer: OPEN then FETCH then LOOP followed by the exit when. If not specified in this order will result in the final return being done twice because of the way the %NOTFOUND is handled by PL/SQL.

8. What are SQLCODE and SQLERRM and why are they important for PL/SQL developers?
Expected answer: SQLCODE returns the value of the error number for the last error encountered. The SQLERRM returns the actual error message for the last error encountered. They can be used in exception handling to report, or, store in an error log table, the error that occurred in the code. These are especially useful for the WHEN OTHERS exception.

9. How can you find within a PL/SQL block, if a cursor is open?
Expected answer: Use the %ISOPEN cursor status variable.

10. How can you generate debugging output from PL/SQL?
Expected answer: Use the DBMS_OUTPUT package. Another possible method is to just use the SHOW ERROR command, but this only shows errors. The DBMS_OUTPUT package can be used to show intermediate results from loops and the status of variables as the procedure is executed. The new package UTL_FILE can also be used.

11. What are the types of triggers?
Expected Answer: There are 12 types of triggers in PL/SQL that consist of combinations of the BEFORE, AFTER, ROW, TABLE, INSERT, UPDATE, DELETE and ALL key words:
BEFORE ALL ROW INSERT
AFTER ALL ROW INSERT
BEFORE INSERT
AFTER INSERT etc.
1. Give one method for transferring a table from one schema to another:
There are several possible methods, export-import, CREATE TABLE... AS SELECT, or COPY.

2. What is the purpose of the IMPORT option IGNORE? What is it?s default setting
The IMPORT IGNORE option tells import to ignore "already exists" errors. If it is not specified the tables that already exist will be skipped. If it is specified, the error is ignored and the tables data will be inserted. The default value is N.

3. You have a rollback segment in a version 7.2 database that has expanded beyond optimal, how can it be restored to optimal
Use the ALTER TABLESPACE ..... SHRINK command.

4. If the DEFAULT and TEMPORARY tablespace clauses are left out of a CREATE USER command what happens? Is this bad or good? Why
The user is assigned the SYSTEM tablespace as a default and temporary tablespace. This is bad because it causes user objects and temporary segments to be placed into the SYSTEM tablespace resulting in fragmentation and improper table placement (only data dictionary objects and the system rollback segment should be in SYSTEM).

5. What are some of the Oracle provided packages that DBAs should be aware of
Oracle provides a number of packages in the form of the DBMS_ packages owned by the SYS user. The packages used by DBAs may include: DBMS_SHARED_POOL, DBMS_UTILITY, DBMS_SQL, DBMS_DDL, DBMS_SESSION, DBMS_OUTPUT and DBMS_SNAPSHOT. They may also try to answer with the UTL*.SQL or CAT*.SQL series of SQL procedures. These can be viewed as extra credit but aren?t part of the answer.

6. What happens if the constraint name is left out of a constraint clause
The Oracle system will use the default name of SYS_Cxxxx where xxxx is a system generated number. This is bad since it makes tracking which table the constraint belongs to or what the constraint does harder.

7. What happens if a tablespace clause is left off of a primary key constraint clause
This results in the index that is automatically generated being placed in then users default tablespace. Since this will usually be the same tablespace as the table is being created in, this can cause serious performance problems.

8. What is the proper method for disabling and re-enabling a primary key constraint
You use the ALTER TABLE command for both. However, for the enable clause you must specify the USING INDEX and TABLESPACE clause for primary keys.

9. What happens if a primary key constraint is disabled and then enabled without fully specifying the index clause
The index is created in the user?s default tablespace and all sizing information is lost. Oracle doesn?t store this information as a part of the constraint definition, but only as part of the index definition, when the constraint was disabled the index was dropped and the information is gone.

10. (On UNIX) When should more than one DB writer process be used? How many should be used
If the UNIX system being used is capable of asynchronous IO then only one is required, if the system is not capable of asynchronous IO then up to twice the number of disks used by Oracle number of DB writers should be specified by use of the db_writers initialization parameter.

11. You are using hot backup without being in archivelog mode, can you recover in the event of a failure? Why or why not
You can?t use hot backup without being in archivelog mode. So no, you couldn?t recover.

12. What causes the "snapshot too old" error? How can this be prevented or mitigated
This is caused by large or long running transactions that have either wrapped onto their own rollback space or have had another transaction write on part of their rollback space. This can be prevented or mitigated by breaking the transaction into a set of smaller transactions or increasing the size of the rollback segments and their extents.

13. How can you tell if a database object is invalid
By checking the status column of the DBA_, ALL_ or USER_OBJECTS views, depending upon whether you own or only have permission on the view or are using a DBA account.

13. A user is getting an ORA-00942 error yet you know you have granted them permission on the table, what else should you check
You need to check that the user has specified the full name of the object (select empid from scott.emp; instead of select empid from emp;) or has a synonym that balls to the object (create synonym emp for scott.emp;)

14. A developer is trying to create a view and the database won?t let him. He has the "DEVELOPER" role which has the "CREATE VIEW" system privilege and SELECT grants on the tables he is using, what is the problem
You need to verify the developer has direct grants on all tables used in the view. You can?t create a stored object with grants given through views.

15. If you have an example table, what is the best way to get sizing data for the production table implementation
The best way is to analyze the table and then use the data provided in the DBA_TABLES view to get the average row length and other pertinent data for the calculation. The quick and dirty way is to look at the number of blocks the table is actually using and ratio the number of rows in the table to its number of blocks against the number of expected rows.

16. How can you find out how many users are currently logged into the database? How can you find their operating system id
There are several ways. One is to look at the v$session or v$process views. Another way is to check the current_logins parameter in the v$sysstat view. Another if you are on UNIX is to do a "ps -efgrep oraclewc -l? command, but this only works against a single instance installation.

17. A user selects from a sequence and gets back two values, his select is:
SELECT pk_seq.nextval FROM dual;What is the problem
Somehow two values have been inserted into the dual table. This table is a single row, single column table that should only have one value in it.

18. How can you determine if an index needs to be dropped and rebuilt
Run the ANALYZE INDEX command on the index to validate its structure and then calculate the ratio of LF_BLK_LEN/LF_BLK_LEN+BR_BLK_LEN and if it isn?t near 1.0 (i.e. greater than 0.7 or so) then the index should be rebuilt. Or if the ratio
BR_BLK_LEN/ LF_BLK_LEN+BR_BLK_LEN is nearing 0.3
1. How can variables be passed to a SQL routine
By use of the & symbol. For passing in variables the numbers 1-8 can be used (&1, &2,...,&8) to pass the values after the command into the SQLPLUS session. To be prompted for a specific variable, place the ampersanded variable in the code itself:
"select * from dba_tables where owner=&owner_name;" . Use of double ampersands tells SQLPLUS to resubstitute the value for each subsequent use of the variable, a single ampersand will cause a reprompt for the value unless an ACCEPT statement is used to get the value from the user.

2. You want to include a carriage return/linefeed in your output from a SQL script, how can you do this
The best method is to use the CHR() function (CHR(10) is a return/linefeed) and the concatenation function "". Another method, although it is hard to document and isn?t always portable is to use the return/linefeed as a part of a quoted string.

3. How can you call a PL/SQL procedure from SQL
By use of the EXECUTE (short form EXEC) command.

4. How do you execute a host operating system command from within SQL
By use of the exclamation ball "!" (in UNIX and some other OS) or the HOST (HO) command.

5. You want to use SQL to build SQL, what is this called and give an example
This is called dynamic SQL. An example would be:
set lines 90 pages 0 termout off feedback off verify off
spool drop_all.sql
select ?drop user ?username? cascade;? from dba_users
where username not in ("SYS?,?SYSTEM?);
spool off
Essentially you are looking to see that they know to include a command (in this case DROP USER...CASCADE;) and that you need to concatenate using the ?? the values selected from the database.

6. What SQLPlus command is used to format output from a select
This is best done with the COLUMN command.

7. You want to group the following set of select returns, what can you group on
Max(sum_of_cost), min(sum_of_cost), count(item_no), item_no
The only column that can be grouped on is the "item_no" column, the rest have aggregate functions associated with them.

8. What special Oracle feature allows you to specify how the cost based system treats a SQL statement
The COST based system allows the use of HINTs to control the optimizer path selection. If they can give some example hints such as FIRST ROWS, ALL ROWS, USING INDEX, STAR, even better.

9. You want to determine the location of identical rows in a table before attempting to place a unique index on the table, how can this be done
Oracle tables always have one guaranteed unique column, the rowid column. If you use a min/max function against your rowid and then select against the proposed primary key you can squeeze out the rowids of the duplicate rows pretty quick. For example:
select rowid from emp e
where e.rowid > (select min(x.rowid)
from emp x
where x.emp_no = e.emp_no);
In the situation where multiple columns make up the proposed key, they must all be used in the where clause.

10. What is a Cartesian product
A Cartesian product is the result of an unrestricted join of two or more tables. The result set of a three table Cartesian product will have x * y * z number of rows where x, y, z correspond to the number of rows in each table involved in the join.

11. You are joining a local and a remote table, the network manager complains about the traffic involved, how can you reduce the network traffic
Push the processing of the remote data to the remote instance by using a view to pre-select the information for the join. This will result in only the data required for the join being sent across.

11. What is the default ordering of an ORDER BY clause in a SELECT statement
Ascending

12. What is tkprof and how is it used
The tkprof tool is a tuning tool used to determine cpu and execution times for SQL statements. You use it by first setting timed_statistics to true in the initialization file and then turning on tracing for either the entire database via the sql_trace parameter or for the session using the ALTER SESSION command. Once the trace file is generated you run the tkprof tool against the trace file and then look at the output from the tkprof tool. This can also be used to generate explain plan output.

13. What is explain plan and how is it used
The EXPLAIN PLAN command is a tool to tune SQL statements. To use it you must have an explain_table generated in the user you are running the explain plan for. This is created using the utlxplan.sql script. Once the explain plan table exists you run the explain plan command giving as its argument the SQL statement to be explained. The explain_plan table is then queried to see the execution plan of the statement. Explain plans can also be run using tkprof.

14. How do you set the number of lines on a page of output? The width
The SET command in SQLPLUS is used to control the number of lines generated per page and the width of those lines, for example SET PAGESIZE 60 LINESIZE 80 will generate reports that are 60 lines long with a line width of 80 characters. The PAGESIZE and LINESIZE options can be shortened to PAGES and LINES.

15. How do you prevent output from coming to the screen
The SET option TERMOUT controls output to the screen. Setting TERMOUT OFF turns off screen output. This option can be shortened to TERM.

16. How do you prevent Oracle from giving you informational messages during and after a SQL statement execution
The SET options FEEDBACK and VERIFY can be set to OFF.

17. How do you generate file output from SQL
By use of the SPOOL command

1. A tablespace has a table with 30 extents in it. Is this bad? Why or why not.
Multiple extents in and of themselves aren?t bad. However if you also have chained rows this can hurt performance.

2. How do you set up tablespaces during an Oracle installation?
You should always attempt to use the Oracle Flexible Architecture standard or another partitioning scheme to ensure proper separation of SYSTEM, ROLLBACK, REDO LOG, DATA, TEMPORARY and INDEX segments.

3. You see multiple fragments in the SYSTEM tablespace, what should you check first?
Ensure that users don?t have the SYSTEM tablespace as their TEMPORARY or DEFAULT tablespace assignment by checking the DBA_USERS view.

4. What are some indications that you need to increase the SHARED_POOL_SIZE parameter?
Poor data dictionary or library cache hit ratios, getting error ORA-04031. Another indication is steadily decreasing performance with all other tuning parameters the same.

5. What is the general guideline for sizing db_block_size and db_multi_block_read for an application that does many full table scans?
Oracle almost always reads in 64k chunks. The two should have a product equal to 64 or a multiple of 64.

6. What is the fastest query method for a table
Fetch by rowid

7. Explain the use of TKPROF? What initialization parameter should be turned on to get full TKPROF output?
The tkprof tool is a tuning tool used to determine cpu and execution times for SQL statements. You use it by first setting timed_statistics to true in the initialization file and then turning on tracing for either the entire database via the sql_trace parameter or for the session using the ALTER SESSION command. Once the trace file is generated you run the tkprof tool against the trace file and then look at the output from the tkprof tool. This can also be used to generate explain plan output.

8. When looking at v$sysstat you see that sorts (disk) is high. Is this bad or good? If bad -How do you correct it?
If you get excessive disk sorts this is bad. This indicates you need to tune the sort area parameters in the initialization files. The major sort are parameter is the SORT_AREA_SIZe parameter.

9. When should you increase copy latches? What parameters control copy latches
When you get excessive contention for the copy latches as shown by the "redo copy" latch hit ratio. You can increase copy latches via the initialization parameter LOG_SIMULTANEOUS_COPIES to twice the number of CPUs on your system.

10. Where can you get a list of all initialization parameters for your instance? How about an indication if they are default settings or have been changed
You can look in the init.ora file for an indication of manually set parameters. For all parameters, their value and whether or not the current value is the default value, look in the v$parameter view.

11. Describe hit ratio as it pertains to the database buffers. What is the difference between instantaneous and cumulative hit ratio and which should be used for tuning
The hit ratio is a measure of how many times the database was able to read a value from the buffers verses how many times it had to re-read a data value from the disks. A value greater than 80-90% is good, less could indicate problems. If you simply take the ratio of existing parameters this will be a cumulative value since the database started. If you do a comparison between pairs of readings based on some arbitrary time span, this is the instantaneous ratio for that time span. Generally speaking an instantaneous reading gives more valuable data since it will tell you what your instance is doing for the time it was generated over.

12. Discuss row chaining, how does it happen? How can you reduce it? How do you correct it
Row chaining occurs when a VARCHAR2 value is updated and the length of the new value is longer than the old value and won?t fit in the remaining block space. This results in the row chaining to another block. It can be reduced by setting the storage parameters on the table to appropriate values. It can be corrected by export and import of the effected table.

13. When looking at the estat events report you see that you are getting busy buffer waits. Is this bad? How can you find what is causing it
Buffer busy waits could indicate contention in redo, rollback or data blocks. You need to check the v$waitstat view to see what areas are causing the problem. The value of the "count" column tells where the problem is, the "class" column tells you with what. UNDO is rollback segments, DATA is data base buffers.

14. If you see contention for library caches how can you fix it
Increase the size of the shared pool.

15. If you see statistics that deal with "undo" what are they really talking about
Rollback segments and associated structures.

16. If a tablespace has a default pctincrease of zero what will this cause (in relationship to the smon process)
The SMON process won?t automatically coalesce its free space fragments.

17. If a tablespace shows excessive fragmentation what are some methods to defragment the tablespace? (7.1,7.2 and 7.3 only)
In Oracle 7.0 to 7.2 The use of the 'alter session set events 'immediate trace name coalesce level ts#';? command is the easiest way to defragment contiguous free space fragmentation. The ts# parameter corresponds to the ts# value found in the ts$ SYS table. In version 7.3 the ?alter tablespace coalesce;? is best. If the free space isn?t contiguous then export, drop and import of the tablespace contents may be the only way to reclaim non-contiguous free space.

18. How can you tell if a tablespace has excessive fragmentation
If a select against the dba_free_space table shows that the count of a tablespaces extents is greater than the count of its data files, then it is fragmented.

19. You see the following on a status report:
redo log space requests 23
redo log space wait time 0
Is this something to worry about? What if redo log space wait time is high? How can you fix this
Since the wait time is zero, no. If the wait time was high it might indicate a need for more or larger redo logs.

20. What can cause a high value for recursive calls? How can this be fixed
A high value for recursive calls is cause by improper cursor usage, excessive dynamic space management actions, and or excessive statement re-parses. You need to determine the cause and correct it By either relinking applications to hold cursors, use proper space management techniques (proper storage and sizing) or ensure repeat queries are placed in packages for proper reuse.

21. If you see a pin hit ratio of less than 0.8 in the estat library cache report is this a problem? If so, how do you fix it
This indicate that the shared pool may be too small. Increase the shared pool size.

22. If you see the value for reloads is high in the estat library cache report is this a matter for concern
Yes, you should strive for zero reloads if possible. If you see excessive reloads then increase the size of the shared pool.

23. You look at the dba_rollback_segs view and see that there is a large number of shrinks and they are of relatively small size, is this a problem? How can it be fixed if it is a problem
A large number of small shrinks indicates a need to increase the size of the rollback segment extents. Ideally you should have no shrinks or a small number of large shrinks. To fix this just increase the size of the extents and adjust optimal accordingly.

24. You look at the dba_rollback_segs view and see that you have a large number of wraps is this a problem
A large number of wraps indicates that your extent size for your rollback segments are probably too small. Increase the size of your extents to reduce the number of wraps. You can look at the average transaction size in the same view to get the information on transaction size.

25. In a system with an average of 40 concurrent users you get the following from a query on rollback extents:
ROLLBACK CUR EXTENTS
--------------------- --------------------------
R01 11
R02 8
R03 12
R04 9
SYSTEM 4
26. You have room for each to grow by 20 more extents each. Is there a problem? Should you take any action
No there is not a problem. You have 40 extents showing and an average of 40 concurrent users. Since there is plenty of room to grow no action is needed.

27. You see multiple extents in the temporary tablespace. Is this a problem
As long as they are all the same size this isn?t a problem. In fact, it can even improve performance since Oracle won?t have to create a new extent when a user needs one.

28. Define OFA.
OFA stands for Optimal Flexible Architecture. It is a method of placing directories and files in an Oracle system so that you get the maximum flexibility for future tuning and file placement.

29. How do you set up your tablespace on installation
The answer here should show an understanding of separation of redo and rollback, data and indexes and isolation os SYSTEM tables from other tables. An example would be to specify that at least 7 disks should be used for an Oracle installation so that you can place SYSTEM tablespace on one, redo logs on two (mirrored redo logs) the TEMPORARY tablespace on another, ROLLBACK tablespace on another and still have two for DATA and INDEXES. They should indicate how they will handle archive logs and exports as well. As long as they have a logical plan for combining or further separation more or less disks can be specified.

30. What should be done prior to installing Oracle (for the OS and the disks)
adjust kernel parameters or OS tuning parameters in accordance with installation guide. Be sure enough contiguous disk space is available.

31. You have installed Oracle and you are now setting up the actual instance. You have been waiting an hour for the initialization script to finish, what should you check first to determine if there is a problem
Check to make sure that the archiver isn?t stuck. If archive logging is turned on during install a large number of logs will be created. This can fill up your archive log destination causing Oracle to stop to wait for more space.

32. When configuring SQLNET on the server what files must be set up
INITIALIZATION file, TNSNAMES.ORA file, SQLNET.ORA file

33. When configuring SQLNET on the client what files need to be set up
SQLNET.ORA, TNSNAMES.ORA

34. What must be installed with ODBC on the client in order for it to work with Oracle
SQLNET and PROTOCOL (for example: TCPIP adapter) layers of the transport programs.

35. You have just started a new instance with a large SGA on a busy existing server. Performance is terrible, what should you check for
The first thing to check with a large SGA is that it isn?t being swapped out.

36. What OS user should be used for the first part of an Oracle installation (on UNIX)
You must use root first.

37. When should the default values for Oracle initialization parameters be used as is
Never

38. How many control files should you have? Where should they be located
At least 2 on separate disk spindles. Be sure they say on separate disks, not just file systems.

39. How many redo logs should you have and how should they be configured for maximum recoverability
You should have at least three groups of two redo logs with the two logs each on a separate disk spindle (mirrored by Oracle). The redo logs should not be on raw devices on UNIX if it can be avoided.

40. You have a simple application with no "hot" tables (i.e. uniform IO and access requirements). How many disks should you have assuming standard layout for SYSTEM, USER, TEMP and ROLLBACK tablespaces
At least 7, see disk configuration answer above.

41. Describe third normal form
Something like: In third normal form all attributes in an entity are related to the primary key and only to the primary key

42. Is the following statement true or false:
"All relational databases must be in third normal form"
False. While 3NF is good for logical design most databases, if they have more than just a few tables, will not perform well using full 3NF. Usually some entities will be denormalized in the logical to physical transfer process.

43. What is an ERD
An ERD is an Entity-Relationship-Diagram. It is used to show the entities and relationships for a database logical model.

44. Why are recursive relationships bad? How do you resolve them
A recursive relationship (one where a table relates to itself) is bad when it is a hard relationship (i.e. neither side is a "may" both are "must") as this can result in it not being possible to put in a top or perhaps a bottom of the table (for example in the EMPLOYEE table you couldn?t put in the PRESIDENT of the company because he has no boss, or the junior janitor because he has no subordinates). These type of relationships are usually resolved by adding a small intersection entity.

45. What does a hard one-to-one relationship mean (one where the relationship on both ends is "must")
Expected answer: This means the two entities should probably be made into one entity.

46. How should a many-to-many relationship be handled
By adding an intersection entity table

47. What is an artificial (derived) primary key? When should an artificial (or derived) primary key be used
A derived key comes from a sequence. Usually it is used when a concatenated key becomes too cumbersome to use as a foreign key.

48. When should you consider denormalization
Whenever performance analysis indicates it would be beneficial to do so without compromising data integrity.

49. How can you determine if an Oracle instance is up from the operating system level
There are several base Oracle processes that will be running on multi-user operating systems, these will be smon, pmon, dbwr and lgwr. Any answer that has them using their operating system process showing feature to check for these is acceptable. For example, on UNIX a ps -efgrep dbwr will show what instances are up.

50. Users from the PC clients are getting messages indicating :
ORA-06114: (Cnct err, can't get err txt. See Servr Msgs & Codes Manual)

What could the problem be
The instance name is probably incorrect in their connection string.

51. Users from the PC clients are getting the following error stack:
ERROR: ORA-01034: ORACLE not available
ORA-07318: smsget: open error when opening sgadef.dbf file.
HP-UX Error: 2: No such file or directory

What is the probable cause
The Oracle instance is shutdown that they are trying to access, restart the instance.

52. How can you determine if the SQLNET process is running for SQLNET V1? How about V2
For SQLNET V1 check for the existence of the orasrv process. You can use the command "tcpctl status" to get a full status of the V1 TCPIP server, other protocols have similar command formats. For SQLNET V2 check for the presence of the LISTENER process(s) or you can issue the command "lsnrctl status".

53. What file will give you Oracle instance status information? Where is it located
The alert.ora log. It is located in the directory specified by the background_dump_dest parameter in the v$parameter table.

54. Users aren?t being allowed on the system. The following message is received:
ORA-00257 archiver is stuck. Connect internal only, until freed
What is the problem
The archive destination is probably full, backup the archive logs and remove them and the archiver will re-start.

55. Where would you look to find out if a redo log was corrupted assuming you are using Oracle mirrored redo logs
There is no message that comes to the SQLDBA or SRVMGR programs during startup in this situation, you must check the alert.log file for this information.

56. You attempt to add a datafile and get:
ORA-01118: cannot add anymore datafiles: limit of 40 exceeded
What is the problem and how can you fix it
When the database was created the db_files parameter in the initialization file was set to 40. You can shutdown and reset this to a higher value, up to the value of MAX_DATAFILES as specified at database creation. If the MAX_DATAFILES is set to low, you will have to rebuild the control file to increase it before proceeding.

57. You look at your fragmentation report and see that smon hasn?t coalesced any of you tablespaces, even though you know several have large chunks of contiguous free extents. What is the problem
Check the dba_tablespaces view for the value of pct_increase for the tablespaces. If pct_increase is zero, smon will not coalesce their free space.

58. Your users get the following error:
ORA-00055 maximum number of DML locks exceeded
What is the problem and how do you fix it
The number of DML Locks is set by the initialization parameter DML_LOCKS. If this value is set to low (which it is by default) you will get this error. Increase the value of DML_LOCKS. If you are sure that this is just a temporary problem, you can have them wait and then try again later and the error should clear.

59. You get a call from you backup DBA while you are on vacation. He has corrupted all of the control files while playing with the ALTER DATABASE BACKUP CONTROLFILE command. What do you do
As long as all datafiles are safe and he was successful with the BACKUP controlfile command you can do the following:
CONNECT INTERNAL
STARTUP MOUNT
(Take any read-only tablespaces offline before next step ALTER DATABASE DATAFILE .... OFFLINE;)
RECOVER DATABASE USING BACKUP CONTROLFILE
ALTER DATABASE OPEN RESETLOGS;
(bring read-only tablespaces back online)
Shutdown and backup the system, then restart
If they have a recent output file from the ALTER DATABASE BACKUP CONTROL FILE TO TRACE; command, they can use that to recover as well.
If no backup of the control file is available then the following will be required:
CONNECT INTERNAL
STARTUP NOMOUNT
CREATE CONTROL FILE .....;
However, they will need to know all of the datafiles, logfiles, and settings for MAXLOGFILES, MAXLOGMEMBERS, MAXLOGHISTORY, MAXDATAFILES for the database to use the command.

Oracle-Explain the difference between a hot backup and a cold backup and the benefits associated with each.

Explain the difference between a hot backup and a cold backup and the benefits associated with each.
A hot backup is basically taking a backup of the database while it is still up and running and it must be in archive log mode. A cold backup is taking a backup of the database while it is shut down and does not require being in archive log mode. The benefit of taking a hot backup is that the database is still available for use while the backup is occurring and you can recover the database to any ball in time. The benefit of taking a cold backup is that it is typically easier to administer the backup and recovery process. In addition, since you are taking cold backups the database does not require being in archive log mode and thus there will be a slight performance gain as the database is not cutting archive logs to disk

What is Difference Between C/C++

C does not have a class/object concept.C++ provides data abstraction, data encapsulation, Inheritance and Polymorphism.C++ supports all C syntax.In C passing value to a function is "Call by Value" whereas in C++ its "Call by Reference"File extension is .c in C while .cpp in C++.(C++ compiler compiles the files with .c extension but C compiler can not!)In C structures can not have contain functions declarations. In C++ structures are like classes, so declaring functions is legal and allowed.C++ can have inline/virtual functions for the classes.c++ is C with Classes hence C++ while in c the closest u can get to an User defined data type is struct and union

What is the difference between run time binding and compile time binding?

Dynamic Binding :The address of the functions are determined at runtime rather than @ compile time. This is also known as "Late Binding".

Static Binding :The address of the functions are determined at compile time rather than @ run time. This is also known as "Early Binding"

What are Templates

C++ Templates allow u to generate families of functions or classes that can operate on a variety of different data types, freeing you from the need to create a separate function or class for each type. Using templates, u have the convenience of writing a single generic function or class definition, which the compiler automatically translates into a specific version of the function or class, for each of the different data types that your program actually uses. Many data structures and algorithms can be defined independently of the type of data they work with. You can increase the amount of shared code by separating data-dependent portions from data-independent portions, and templates were introduced to help you do that.

C-What is Operator overloading

When an operator is overloaded, it takes on an additional meaning relative to a certain class. But it can still retain all of its old meanings.Examples:1) The operators >> and << may be used for I/O operations because in the header, they are overloaded.2) In a stack class it is possible to overload the + operator so that it appends the contents of one stack to the contents of another. But the + operator still retains its original meaning relative to other types of data.

What is Polymorphism

'Polymorphism' is an object oriented term. Polymorphism may be defined as the ability of related objects to respond to the same message with different, but appropriate actions. In other words, polymorphism means taking more than one form. Polymorphism leads to two important aspects in Object Oriented terminology - Function Overloading and Function Overriding. Overloading is the practice of supplying more than one definition for a given function name in the same scope. The compiler is left to pick the appropriate version of the function or operator based on the arguments with which it is called. Overriding refers to the modifications made in the sub class to the inherited methods from the base class to change their behavior.

C-C++-interview questions- CPLUS interview Questions

1. Is it possible to have Virtual Constructor? If yes, how? If not, Why not possible ?There is nothing like Virtual Constructor. The Constructor cant be virtual as the constructor is a code which is responsible for creating a instance of a class and it cant be delegated to any other object by virtual keyword means.
2. What about Virtual Destructor?Yes there is a Virtual Destructor. A destructor can be virtual as it is possible as at runtime depending on the type of object baller is balling to , proper destructor will be called.
3. What is Pure Virtual Function? Why and when it is used ?The abstract class whose pure virtual method has to be implemented by all the classes which derive on these. Otherwise it would result in a compilation error.This construct should be used when one wants to ensure that all the derived classes implement the method defined as pure virtual in base class.
4. What is problem with Runtime type identification?The run time type identification comes at a cost of performance penalty. Compiler maintains the class.
5. How Virtual functions call up is maintained?Through Look up tables added by the compile to every class image. This also leads to performance penalty.
6. Can inline functions have a recursion?No.Syntax wise It is allowed. But then the function is no longer Inline. As the compiler will never know how deep the recursion is at compilation time.
7. How do you link a C++ program to C functions?By using the extern "C" linkage specification around the C function declarations.Programmers should know about mangled function names and type-safe linkages. Then they should explain how the extern "C" linkage specification statement turns that feature off during compilation so that the linker properly links function calls to C functions.
8. Explain the scope resolution operator?It permits a program to reference an identifier in the global scope that has been hidden by another identifier with the same name in the local scope.
9. How many ways are there to initialize an int with a constant?1. int foo = 123;2. int bar(123);
10. What is your reaction to this line of code? delete this;It is not a good programming Practice.A good programmer will insist that you should absolutely never use the statement if the class is to be used by other programmers and instantiated as static, extern, or automatic objects. That much should be obvious.The code has two built-in pitfalls. First, if it executes in a member function for an extern, static, or automatic object, the program will probably crash as soon as the delete statement executes. There is no portable way for an object to tell that it was instantiated on the heap, so the class cannot assert that its object is properly instantiated. Second, when an object commits suicide this way, the using program might not know about its demise. As far as the instantiating program is concerned, the object remains in scope and continues to exist even though the object did itself in. Subsequent dereferencing of the baller can and usually does lead to disaster. I think that the language rules should disallow the idiom, but that's another matter.
11. What is the difference between a copy constructor and an overloaded assignment operator?A copy constructor constructs a new object by using the content of the argument object. An overloaded assignment operator assigns the contents of an existing object to another existing object of the same class.
12. When should you use multiple inheritance?There are three acceptable answers:- "Never," "Rarely," and "When the problem domain cannot be accurately modeled any other way."
Consider an Asset class, Building class, Vehicle class, and CompanyCar class. All company cars are vehicles. Some company cars are assets because the organizations own them. Others might be leased. Not all assets are vehicles. Money accounts are assets. Real estate holdings are assets. Some real estate holdings are buildings. Not all buildings are assets. Ad infinitum. When you diagram these relationships, it becomes apparent that multiple inheritance is a likely and intuitive way to model this common problem domain. The applicant should understand, however, that multiple inheritance, like a chainsaw, is a useful tool that has its perils, needs respect, and is best avoided except when nothing else will do.
13. What is a virtual destructor?The simple answer is that a virtual destructor is one that is declared with the virtual attribute.The behavior of a virtual destructor is what is important. If you destroy an object through a baller or reference to a base class, and the base-class destructor is not virtual, the derived-class destructors are not executed, and the destruction might not be comple
14. Can a constructor throw a exception? How to handle the error when the constructor fails?The constructor never throws a error.
15. What are the debugging methods you use when came across a problem?Debugging with tools like :
GDB, DBG, Forte, Visual Studio.
Analyzing the Core dump.
Using tusc to trace the last system call before crash.
Putting Debug statements in the program source code.
16. How the compilers arranges the various sections in the executable image?The executable had following sections:-
Data Section (uninitialized data variable section, initialized data variable section )
Code Section
Remember that all static variables are allocated in the initialized variable section.
17. Explain the ISA and HASA class relationships. How would you implement each in a class design?A specialized class "is" a specialization of another class and, therefore, has the ISA relationship with the other class.This relationship is best implemented by embedding an object of the Salary class in the Employee class.
18. When is a template a better solution than a base class?When you are designing a generic class to contain or otherwise manage objects of other types, when the format and behavior of those other types are unimportant to their containment or management, and particularly when those other types are unknown (thus, the generality) to the designer of the container or manager class.
19. What are the differences between a C++ struct and C++ class?The default member and base-class access specifies are different.This is one of the commonly misunderstood aspects of C++. Believe it or not, many programmers think that a C++ struct is just like a C struct, while a C++ class has inheritance, access specifies, member functions, overloaded operators, and so on. Actually, the C++ struct has all the features of the class. The only differences are that a struct defaults to public member access and public base-class inheritance, and a class defaults to the private access specified and private base-class inheritance.
20. How do you know that your class needs a virtual destructor?If your class has at least one virtual function, you should make a destructor for this class virtual. This will allow you to delete a dynamic object through a baller to a base class object. If the destructor is non-virtual, then wrong destructor will be invoked during deletion of the dynamic object.
21. What is the difference between new/delete and malloc/free?Malloc/free do not know about constructors and destructors. New and delete create and destroy objects, while malloc and free allocate and deallocate memory.
22. What happens when a function throws an exception that was not specified by an exception specification for this function?Unexpected() is called, which, by default, will eventually trigger abort().
23. Can you think of a situation where your program would crash without reaching the breakball, which you set at the beginning of main()?C++ allows for dynamic initialization of global variables before main() is invoked. It is possible that initialization of global will invoke some function. If this function crashes the crash will occur before main() is entered.
24. What issue do auto_ptr objects address?If you use auto_ptr objects you would not have to be concerned with heap objects not being deleted even if the exception is thrown.
25. Is there any problem with the following:char *a=NULL; char& p = *a;?The result is undefined. You should never do this. A reference must always refer to some object.
26. Why do C++ compilers need name mangling?Name mangling is the rule according to which C++ changes function's name into function signature before passing that function to a linker. This is how the linker differentiates between different functions with the same name.
27. Is there anything you can do in C++ that you cannot do in C?
No. There is nothing you can do in C++ that you cannot do in C. After all you can write a C++ compiler in C

What are the major differences between C and C++?
What are the differences between new and malloc?
What is the difference between delete and delete[]?
What are the differences between a struct in C and in C++?
What are the advantages/disadvantages of using #define?
What are the advantages/disadvantages of using inline and const?
What is the difference between a baller and a reference?
When would you use a baller? A reference?
What does it mean to take the address of a reference?
What does it mean to declare a function or variable as static?
What is the order of initalization for data?
What is name mangling/name decoration?
What kind of problems does name mangling cause?
How do you work around them?
What is a class?
What are the differences between a struct and a class in C++?
What is the difference between public, private, and protected access?
For class CFoo { }; what default methods will the compiler generate for you>?
How can you force the compiler to not generate them?
What is the purpose of a constructor? Destructor?
What is a constructor initializer list?
When must you use a constructor initializer list?
What is a:
Constructor?
Destructor?
Default constructor?
Copy constructor?
Conversion constructor?
What does it mean to declare a...
member function as virtual?
member function as static?
member function as static?
member variable as static?
destructor as static?
Can you explain the term "resource acquisition is initialization?"
What is a "pure virtual" member function?
What is the difference between public, private, and protected inheritance?
What is virtual inheritance?
What is placement
new?
What is the difference between
operator new
and the
new
operator?
What is exception handling?
Explain what happens when an exception is thrown in C++.
What happens if an exception is not caught?
What happens if an exception is throws from an object's constructor?
What happens if an exception is throws from an object's destructor?
What are the costs and benefits of using exceptions?
When would you choose to return an error code rather than throw an exception?
What is a template?
What is partial specialization or template specialization?
How can you force instantiation of a template?
What is an iterator?
What is an algorithm (in terms of the STL/C++ standard library)?
What is
std::auto_ptr?
What is wrong with this statement?
std::auto_ptr ptr(new char[10]);
It is possible to build a C++ compiler on top of a C compiler. How would you do this?