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by using the delete operation some consisting records can be deleted from a relation to delete some definite records from the database a condition is
1 insertlt1 vipin 20 mayur vihargt into personviolated constraint - key constraintreason - primary key 1 already exists in
update operations and dealing with constraint violationsthere are three basic operations to be executes on relations insertion deletion updatethe
it defines that no primary key value can be null this is as the primary key is used to recognize individual tuple in the relation so we will not be
this constraint shows that the key attribute value in each tuple must be unique ie no two tuples have the similar value for the key attribute this is
domain constraintit shows that each attribute in a relation has to contain an atomic value only from the corresponding domains the data types
relational and e-r modelthere are three types of constraints on relational database that have domain constraint primary key constraint integrity
super keys of a relation can have extra attributes candidate keys are minimal super key ie such a key have no extraneous attribute an attribute is
a super key is an attribute or set of attributes used to recognize the records uniquely in a relationfor instance in the relation person defines
in a relation tuples are not inserted in any definite order ordering of tuples is not defined as a part of a relation definition though records may
examplerelational schema for personperson personid integer name string age integer address stringrelation instancein this instance m 3 and n
examplerelation schema for studentstudent roll no string name string login string age integer relation
a relation instance indicates as r is a collection of tuples for a given relational schema at a exact point of timea relation state r of the relation
a relation has relational schema relation instancerelational schemaa relational schema shows the relations name its attributes and the domain of
a domain is a set of permissible values that can be given to an attribute so each attribute in a table has a definite domain values to these
before we talk about the relational model in more detail let us first define some very basic terms used in this modeltupleevery row in a table shows
a model in database system mostly defines the organisation of data or structure and a set of operations on that data relational model is a easy model
in the first unit of this block you have been given with the details of the database management system its structure advantages etc this unit is an
record based logical models use records as the key data representation componentsexamplesrelational model it shows data as well as relationship
object-based models use objects as key data representation componentsexamples- entity-relationship model it is a collection of real world
after going by the database architecture let us now dwell on an important query how is the data organised in a database there are a lot of basic
these permit the user to unload a database or parts of a database and reload the data on the similar machine or on another machine in a dissimilar
these are designed to reduce the effects of a database failure and make sure a database is restored to a consistent state if a failure does arise
these are interactive interfaces graphical that hide the difficulty of the dbms and query language behind an intuitive simple to understand and
command line interfaces these are interactive interfaces character-based that let you use the complete power and functionality of the dbms query