Oracle – Technical FAQ – Part 4


 Q18.) What are the OOPS concepts in Oracle?

A18.) Oracle does implement the OOPS concepts. The best example is the Property Classes. We can categorise the properties by setting the visual attributes and then attach the property classes for the objects. OOPS supports the concepts of objects and classes and we can consider the property classes as classes and the items as objects.

 

Q19) What is the difference between candidate key, unique key and primary key?

A19) Candidate keys are the columns in the table that could be primary keys and the primary key is the key that has been selected to identify the rows. Unique key is also useful for identifying the distinct rows in the table.

 

Q20) What is concurrency?

A20) Concurrency is allowing simultaneous access of same data by different users. Locks useful for accessing the database are

a) Exclusive — The exclusive lock is useful for locking the row when an insert , update or delete is being done. This lock should not be applied when we do only select from the row.

b) Share lock — We can do the table as Share_Lock as many share_locks can be put on the same resource.

 

Q21) What are the Previleges and Grants?

A21) Privileges are the right to execute a particular type of SQL statements. The grant has to be given by the owner to object.

 

Q22) What are Table Space, Data files, parameter file, control files?

A22) Table space: The table space is useful for storing the data in the database. When a database is created two table spaces are created.

a) System Table space : This data file stores all the tables related to the system and dba tables.

b) User Table Space: This data file stores all the user related tables.

We should have separate table spaces for storing the tables and indexes so that the access is fast.

Data files : Every oracle Data base has one or more physical data files. They store the data for the database. Every datafile is associated with only one database. Once the data file is created the size can not change. To increase the size of the database to store more data we have to add data file.

Parameter file:Parameter file is needed to start an instance. A parameter file contains the list of instance configuration parameters e.g. db_block_buffers = 500

db_name = ORA7

db_domain = u.s.acme lang

Control files : Control files record the physical structure of the data files and redo log files . They contain the DB name, name and locations of dbs , data files, redo log files and time stamp.

 

Q23) What is physical storage of the Data?

A23) The finest level of granularity of the data base are the blocks.

Extent : Extent is the number of specific number of contigious data blocks.

Segments : Set of Extents allocated for Extents. There are three types of segments

a) Data Segment : Non clustered tables has data segment data of every table is stored in cluster data segment.

b) Index Segment : Each index has index segment that stores data.

c) Rollback Segment : Temporarily store ‘undo’ information.

 

Q24) What is Normalisation ? Explain 1NF, 2NF, 3NF.

Normalization is a process of eliminating data redudancy.

1NF- No repeating groups.

2NF- Eliminates the functional dependency on the partial key field.

3NF- Eliminates the functional dependency on the non-key field.

Oracle – Technical FAQ – Part 2


Q6) What are the database triggers and stored procedures?
A6) Database triggers are procedures that are automatically executed as a result of insert in, update to or delete from table.
Database triggers have the values old and new to denote the old value in the table before it is deleted and the new indicated the new value that will be used. DT are useful for implementing complex business rules which can not be enforced using the integrity rules. We can have the trigger as before trigger or after trigger and at statement or row level.
e.g. operations insert, update, delete — 3
before, after 3 * 2 — a total of 6 combinations

At statement level (once for the trigger) or row level (for every execution) 6 * 2 — a total of 12.

Thus a total of 12 combinations are there and the restriction of usage of 12 triggers has been lifted from Oracle 7.3 onwards

Stored Procedures : Stored procedures are procedures that are stored in complied form in the database. The advantage of using the stored procedures is that many users can use the same procedure in compiled and ready to use format.

 

Q7) How many integrity rules are there and what are they?

A7) There are three integrity rules and they are as follows

a)Entity integrity Rule : The entity integrity rule enforces that the primary key can not be Null

b) Foreign key integrity rule : The FKIR denotes that the relationship between the foreign key and the primary key has to be enforced. When there is data in child tables the master tables can not be deleted.

c) Business integrity rules : The third integrity rule is about the complex business processes which can not be implemented by the above 2 rules.

 

Q.8.) What are the various Master and Detail relationships?

A.8.) The various Master and Detail relationship are

a) Non Isolated : The Master can not be deleted when a child is existing

b) Isolated : The master can be deleted when the child is existing

c) Cascading : The child gets deleted when the master is deleted.

 

Q9) What are the various Block Coordination properties ?.

A9) The various block coordination properties are

a) Immediate – Default setting. The detail records are shown when the Master Record are shown.

b) Differed with AutoQuery — Oracle forms defer fetching the detail records until the operator navigates to the detail block.

C) Deffered with no auto query — The operator must navigate to the detail block and explicitly executes a query.

 

Q10) What are the different Optimisation techniques ?

A10) The various optimisation techniques are

a) Execute plan : We can see the plan of the query and change it accordingly based on the indexes

b) Optimizer_hint : Set_item_property (‘DeptBlock’,OPTIMIZER_HINT,’FIRST_ROWS’);

Select /* + First Rows */ Deptno, Dname, Loc, Rowid from dept

where (Deptno > 25)

c) Optimize_sql : By setting the optimize_sql = No, Oracle Forms assign a single cursor for all SQL statements. This slow downs the processing because for everytime the SQL must be parsed whenever they are executed. f45run module = my_firstform useid = scott/tiger optimize_Tp = No

 

  more questions are here : https://knoworacle.wordpress.com/2008/06/08/oracle-technical-faq-part-2/

Part 3 is here :   https://knoworacle.wordpress.com/2008/06/09/oracle-technical-faq-part-3/

Part 1 is here : https://knoworacle.wordpress.com/2008/08/11/oracle-technical-faq-part-1

 

 

 

Oracle – Technical FAQ – Part 1


Q1) What are the background processes in Oracle and what are they?
Ans: This is one of the most frequently asked question. There are basically 9 processes but in a general system we need t mention the first five background processes. They do the house keeping activities for the Oracle and are common in any system
The various background processes in oracle are
a) Data base writer (DBWR) : Data Base Writer writes modified blocks from databas buffer cache to Datafiles. This is required since the data is not written whenever a transaction is commited.

b) LogWriter(LGWR) : LogWriter writes the redo log entries to disk. Redo log data is generated in redo log buffer of SGA. As transaction commits and logs buffer fills, LGWR writes log entries into a online redo log file.

c) System Monitor (SMON) : The System Monitor performs instance recovery at instance startup. This is useful for recovery from system failure.

d) Process Monitor (PMON) : The Process Monitor performs process recovery when user process fails. Pmon clears and frees resources that process was using.

e) CheckPoint (CKPT): At specified times, all modified database buffers in SGA are written to data files by DBWR at checkpoints and updating all data files and control files of database to indicate the most recent checkpoint.

f) Archiever (ARCH) : The archiever copies online redo log files to archival storal when they are busy.

g) recoveror (RECO) : The recoveror is used to reslove the distributed transaction in network.

h) Dispatcher (Dnnn) : The Dispatcher is useful in Multi Threaded Architecture.

i) Lckn : We can have upto 10 lock processed for inter instance locking in parallel sql.

Q2) How many types of sql statements are there in Oracle?

A2) There are basically 6 types of sql statements. They are

a) Data defination Language (DDL) : The DDL statements define and maintain objects and drop objects.

b) Data Manipulation Language (DML) : The DML statements manipulate database data

c) Transaction Control Statements : Manage change by DML

d) Session Control : Used to control the properties of current session enabling and disabling roles and changing e.g. Alter statements , Set Role

e) System Control Statements : Change properties of Oracle Instance e.g. Alter System

f) Embedded Sql : Incorporate DDL, DML and TCS in processing Languagel e.g. Using the SQL statements in language such as ‘C’, Open, Fetch, Execute and close

Q3) What is a transaction in Oracle ?

A3) A transaction is a logical unit of work that compromises one or more SQL statements executed by a simple user. According to ANSI, a transaction begins with first executable statement and ends when it is explicitly commited or rolled back.

Q4) What are the key words used in Oracle?

A4) The key words that are used in Oracle are

a) Commiting : A transaction is said to be commited when the transaction makes permanent changes resulting from the SQL statements

b) Rollback : A transaction that retracts any of the changes resulting from SQL statements in Transaction.

c) Savepoint : For long transactions that contain many SQL statements , intermediate markers or savepoints are declared. Savepointes can be used to divide a transaction into smaller points.

d) Rolling forward : Process of applying redo log during recovery is called rolling forward.

e) Cursor : A cursor is a handle (name or a pointer) for the memory associated with a specific statement. A cursor is basically an area allocated by Oracle for executing the SQL statement. Oracle uses an implicit cursor statement for single row query and uses Explicit cursor for a multirow query.

f) System Global Area (SGA) : The SGA is a shared memory region allocated by the Oracle that contains Data and control information for one Oracle Instance. It consists of Database buffre cache and redo log buffer.

g) Program Global Area (PGA) : The PGA is a memory buffer that contains data and control information for server process.

h) Database Buffer Cache : Database buffer of SGA stores he most recently used blcoks of database data. The set of database buffers in an instance is called Database Buffer Cache.

i) Redo log buffer : Redo log buffer of SGA stores all the redo log entries.

j) Redo log files :Redo log files are set of files that protect altered database in memory that has been not written to Data files. They are basically used for backup when a database crashes.

k) Process : A process is a ‘thread of control’ or mechanism in Operating System that executes series of steps

Q5) What are procedures, functions and packages?

A5) Procedures and functions consist of set of PL/SQL statements that are grouped together as a unit to solve a specific problem or perform a set of related tasks.

Procedure do not return values while functions return one and only one value.

Packages provide a method of encapsulating and storing related procedures, functions and other package contents.

 more questions are here : https://knoworacle.wordpress.com/2008/06/08/oracle-technical-faq-part-2/

Part 3 is here :   https://knoworacle.wordpress.com/2008/06/09/oracle-technical-faq-part-3/

 

 

 

Oracle – Technical FAQ – Part 3


Q11) How do you implement the If statement in the select statement?
A11) We can implement the if statement in the select statement by using the decode statement.
e.g. select DECODE(EMP_CAT,’1′,’First’,’2′,’Second’,Null);
Here the Null is the else statement where null is done.
 
Q12) How many types of exceptions are there?

A12) a) System exceptions

e.g. When no_data_found, when too_many_rows

b) User Defined Exception

e.g. When my_exception then

 

Q13) What are the inline and the precompiler directives ?

A13) The inline and precompiler directives detect the values directly.

 

Q14) How do you use the same lov for 2 columns ?

A14) We can use the same lov for 2 columns by passing the return values in global values and using the global values in the code.

 

Q15) How many minimum groups are required for a matrix report ?

A15) The minimum number of groups in matrix report are 4.

 

Q16) What is the difference between the static and dynamic lov?

A16) The static lov contains the predetermined values while the dynamic lov contains values that come at run time.

 

Q17) What are snap shots and views ?

A17) Snapshots are mirror or replicas of tables. Views are build using the columns from one or more tables. The single table view can be updated but the view with multi table can not be updated.