What are the components of logical database structure of Oracle database?
The Logical Database Structure of an Oracle include :
> The schema objects,
> Data blocks,
> Segments and
> schema objects : means table, index, synonyms, sequences etc.
> Data blocks : are the smallest part of the oracle database defined by DB_BLOCK_SIZE parameter.
> Extent : A group of data blocks forms an extent.
> Segments : An extents groups tends to segments,
> Table space : lastly a group of segment forms a tablespace.Reply
What are the components of physical database structure of Oracle database?
Physical components of oracle database are:
> Control files,
> Redo log files and
> Control file : control file is basicaly a type of file .Its read in the mount state of database. control file is a small binary file which records the physical structure of database which includes
* Database name
* names and locations of datafiles and online
redo log files.
* timestamp of database creation
* check point information
* current log sequence number.
Redo log files : Redo log files usually use for the saving to the files. This files saves all the changes that are made to the database as they occur. This plays a great role in the database recovery.
Datafiles : Datafiles are the physicalfiles which stores data of all logical structure.Reply
What is SQL?
SQL is a bassically standard language for accessing and manipulating databases. Its is defines as :
> SQL stands for Structured Query Language
> SQL lets you access and manipulate databases
> SQL is an ANSI (American National Standards Institute) standard.
SQL have a many properties, It can do :
> SQL can execute queries against a database.
> SQL can retrieve data from a database.
> SQL can insert records in a database.
> SQL can update records in a database.
> SQL can delete records from a database.
> SQL can create new databases.
> SQL can create new tables in a database.
> SQL can create stored procedures in a database.
> SQL can create views in a database.
> SQL can set permissions on tables, procedures,
What is Index?
An index is a physical structure containing pointers to the data. Indices are created in an existing table to locate rows more quickly and efficiently. It is possible to create an index on one or more columns of a table, and each index is given a name. The users cannot see the indexes, they are just used to speed up queries. Effective indexes are one of the best ways to improve performance in a database application
. A table scan happens when there is no index available to help a query. In a table scan SQL Server examines every row in the table to satisfy the query results. Table scans are sometimes unavoidable, but on large tables, scans have a terrific impact on performance.Reply
What is View?
A simple view can be thought of as a subset of a table. It can be used for retrieving data, as well as updating or deleting rows. Rows updated or deleted in the view are updated or deleted in the table the view was created with. It should also be noted that as data in the original table changes, so does data in the view, as views are the way to look at part of the original table. The results of using a view are not permanently stored in the database. The data accessed through a view is actually constructed using standard T-SQL select command and can come from one to many different base tables or even other views.Reply
What is Trigger?
A trigger is a SQL procedure that initiates an action when an event (INSERT, DELETE or UPDATE) occurs. Triggers are stored in and managed by the DBMS.Triggers are used to maintain the referential integrity of data by changing the data in a systematic fashion. A trigger cannot be called or executed; the DBMS automatically fires the trigger as a result of a data modification to the associated table. Triggers can be viewed as similar to stored procedures in that both consist of procedural logic that is stored at the database level. Stored procedures, however, are not event-drive and are not attached to a specific table as triggers are. Stored procedures are explicitly executed by invoking a CALL to the procedure while triggers are implicitly executed. In addition, triggers can also execute stored procedures.
Nested Trigger: A trigger can also contain INSERT, UPDATE and DELETE logic within itself, so when the trigger is fired because of data modification it can also cause another data modification, thereby firing another trigger. A trigger that contains data modification logic within itself is called a nested trigger.Reply
What is Stored Procedure
A stored procedure is a named group of SQL statements that have been previously created and stored in the server database. Stored procedures accept input parameters so that a single procedure can be used over the network by several clients using different input data. And when the procedure is modified, all clients automatically get the new version. Stored procedures reduce network traffic and improve performance. Stored procedures can be used to help ensure the integrity of the database.
e.g. sp_helpdb, sp_renamedb, sp_depends etcReply
What is normalization?
Normalisation is a process whish is the tables in a database are optimised to remove the potential for redundancy. Two main problems may arise if this is not done:
> Repeated data makes a database bigger.
> Multiple instances of the same values make
maintaining the data more difficult and can
What are different normalization forms?
normalisation have a se veral forms that a database structure can be subject to, each with rules that constrain the database further and each creating what is called a Normal Form. These are, in order:
> First Normal Form (1NF)
> Second Normal Form (2NF)
> Third Normal Form (3NF)
> Boyce Codd Normal Form (BCNF)
> Fourth Normal Form (4NF)
> Fifth Normal Form (5NF)
> Optimal Normal Form (ONF)
> Domain-Key Normal Form (DKNF)
Theses are defined as :
> 1NF: Eliminate Repeating Groups : Make a separate table for each set of related attributes, and give each table a primary key. Each field contains at most one value from its attribute domain.
> 2NF: Eliminate Redundant Data : If an attribute depends on only part of a multi-valued key, remove it to a separate table.
> 3NF: Eliminate Columns Not Dependent On Key : If attributes do not contribute to a description of the key, remove them to a separate table. All attributes must be directly dependent on the primary key.
> BCNF: Boyce-Codd Normal Form : If there are non-trivial dependencies between candidate key attributes, separate them out into distinct tables.
> 4NF: Isolate Independent Multiple Relationships : No table may contain two or more 1:n or n:m relationships that are not directly related.
> 5NF: Isolate Semantically Related Multiple : Relationships There may be practical constrains on information that justify separating logically related many-to-many relationships.
> ONF: Optimal Normal Form : A model limited to only simple (elemental) facts, as expressed in Object Role Model notation.
> DKNF: Domain-Key Normal Form : A model free from all modification anomalies.Reply
What is RDBMS?
RDBMS stands for Relational Database Management
System. RDBMS is the basis for SQL, and for all
modern database systems like MS SQL Server, IBM
DB2, Oracle, MySQL, and Microsoft Access. The data in RDBMS is stored in database objects
called tables. A table is a collections of
related data entries and it consists of columns
and rows.Relational Data Base Management Systems
(RDBMS) are database management systems that maintain data records and indices in tables. Relationships may be created and maintained across and among the data and tables. In a relational database, relationships between data items are expressed by means of tables. Interdependencies among these tables are expressed by data values rather than by pointers. This allows a high degree of data independence. An RDBMS has the capability to recombine the data items from different files, providing powerful tools for data usage.Reply