RDBMS (Relational Database Management System)
RDBMS stands for Relational
Database Management System. RDBMS data is structured in database tables, fields
and records. Each RDBMS table consists of database table rows. Each database
table row consists of one or more database table fields.
RDBMS store the data into collection of tables,
which might be related by common fields (database table columns). RDBMS also
provide relational operators to manipulate the data stored into the database
tables.
DBMS
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.A
Relational database management system (RDBMS) is a database management system
(DBMS) that is based on the relational model as introduced by E. F. Codd.
Table
The
data in RDBMS is stored in database objects called tables. The
table is a collection of related data entries and it consists of columns and
rows.
Field
Every table is broken up into
smaller entities called fields. The fields in the CUSTOMERS table consist of
ID, NAME, AGE, ADDRESS and SALARY.
A field is a column in a table
that is designed to maintain specific information about every record in the
table.
Record
A record, also called a row of
data, is each individual entry that exists in a table.
Column
A column is a vertical entity in
a table that contains all information associated with a specific field in a
table.
NULL
A
NULL value in a table is a value in a field that appears to be blank, which
means a field with a NULL value is a field with no value.
It is very important to
understand that a NULL value is different than a zero value or a field that
contains spaces. A field with a NULL value is one that has been left blank
during record creation.
SQL Constraints
Constraints are the rules
enforced on data columns on table. These are used to limit the type of data
that can go into a table. This ensures the accuracy and reliability of the data
in the database.
Constraints could be column level
or table level. Column level constraints are applied only to one column where
as table level constraints are applied to the whole table.
Following are commonly used
constraints available in SQL:
·
NOT NULL Constraint: Ensures that a column cannot have NULL
value.
·
DEFAULT Constraint: Provides a default value for a column when
none is specified.
·
UNIQUE Constraint: Ensures that all values in a column are
different.
·
PRIMARY Key: Uniquely identified each rows/records in a
database table.
·
FOREIGN Key: Uniquely identified a rows/records in any another
database table.
·
CHECK Constraint: The CHECK constraint ensures that all values
in a column satisfy certain conditions.
·
INDEX: Use to create and retrieve data from the database very
quickly.
Data Integrity:
The following categories of the
data integrity exist with each RDBMS:
·
Entity Integrity: There are no duplicate rows in a table.
·
Domain Integrity: Enforces valid entries for a given column by restricting
the type, the format, or the range of values.
·
Referential integrity: Rows cannot be deleted, which are used by other records.
·
User-Defined Integrity: Enforces some specific business rules that do not fall
into entity, domain or referential integrity.
Database Normalization
Database normalization is the
process of efficiently organizing data in a database. There are two reasons of
the normalization process:
·
Eliminating redundant data, for
example, storing the same data in more than one tables.
·
Ensuring data dependencies make
sense.
Both of these are worthy goals as
they reduce the amount of space a database consumes and ensure that data is
logically stored. Normalization consists of a series of guidelines that help
guide you in creating a good database structure.
Normalization guidelines are
divided into normal forms; think of form as the format or the way a database
structure is laid out. The aim of normal forms is to organize the database
structure so that it complies with the rules of first normal form, then second
normal form, and finally third normal form.
It's your choice to take it
further and go to fourth normal form, fifth normal form, and so on, but
generally speaking, third normal form is enough.
MySQL
MySQL is an open source SQL
database, which is developed by Swedish company MySQL AB. MySQL is pronounced
"my ess-que-ell," in contrast with SQL, pronounced
"sequel."
MySQL is supporting many
different platforms including Microsoft Windows, the major Linux distributions,
UNIX, and Mac OS X.
MySQL has free and paid versions,
depending on its usage (non-commercial/commercial) and features. MySQL comes
with a very fast, multi-threaded, multi-user, and robust SQL database server.
ORACLE
It is a very large and multi-user
database management system. Oracle is a relational database management system
developed by 'Oracle Corporation'.
Oracle works to efficiently
manage its resource, a database of information, among the multiple clients
requesting and sending data in the network.
It is an excellent database
server choice for client/server computing. Oracle supports all major operating
systems for both clients and servers, including MSDOS, NetWare, UnixWare, OS/2
and most UNIX flavors.
Operator
An operator is a reserved word or
a character used primarily in an SQL statement's WHERE clause to perform
operation(s), such as comparisons and arithmetic operations.
Operators are used to specify
conditions in an SQL statement and to serve as conjunctions for multiple
conditions in a statement.
·
Arithmetic operators
·
Comparison operators
·
Logical operators
·
Operators used to negate
conditions
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