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A primary key is the identifier in a table. It cannot contain values that are null, and it has to be unique for every record. For example, a driver's license number could be a primary key in a relational database table. Every driver is assigned to one unique identifier, or driver's license number, and no two driver's license numbers are identical.
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What are the main characteristics of a relation in DBMS?
In a Database Management System (DBMS), a relation is represented as a table consisting of rows and columns. Each row, or tuple, corresponds to a unique record, while each column, or attribute, represents a specific data field. Relations must adhere to the principles of atomicity, meaning each attribute should hold indivisible values, and they must maintain a unique identifier, usually a primary key, to distinguish each record. Additionally, all entries in a column should be of the same data type, ensuring consistency within the relation.
Difference between composite and primary key?
There are two types of keys in any database; composite and primary keys. Composite key differs from primary key in that it contains more than one column while primary key is composed of only one field and cannot have a null value.
What is Relationship between a primary and a foreign key?
A primary key is one or more colums in a table whose values would uniquely identify a row in that table. A foreign key is a one or more columns in one table that are used to reference rows in another table. In a properly designed 3NF schema, the foreign key columns should correspond to the primary key columns of the table being referenced.
Is a foreign key field always on the one side of a one-to-many relationship between two tables?
No. The foreign key is always on the many side. A foreign key is a field that is a primary key in another table, not in the table it is in. It can therefore be repeated in the table it is, so it can act as the many side. In its own table, it is the primary key, and only appears once.
Diffentiate between full and partial dependency?
Full Dependency:Given a relation R and functional dependency x->y (y is fully functionally dependent on x)there is no any z->y ,where Z is a proper subset of xPartial Dependency:If any proper subset of the key determine any of the non-key attributes then there exist a partial dependency p q->c d (p q is the primary key)p->cq->cp->dq->d
Why do you designate one of the candidate key of relation to be the primary key?
We designate one of the candidate key of a relation to be a primary key because that primary key is use for any foreign key references.
What are the requirements for a relation to be in Second Normal Form?
A relation is in second normal form (2NF) if any of the following conditions apply: The primary key consists of only one attribute No non-primary key attribute exists in the relation Every non-primary key attribute is functionally dependent on the full set of primary key attributes
How do you convert weak entities to relations?
To convert weak entities to relations in a database schema, you first need to identify the weak entity's identifying relationship with its owner entity. This involves including a foreign key in the weak entity that references the primary key of the owner entity. Additionally, the weak entity should have its own primary key, typically created by combining its partial key with the primary key of the owner entity. Finally, this new relation can be established in the relational schema, ensuring that the weak entity can now be uniquely identified.
What are the functions of a primary key?
It is a contraint(checks) provided by DBMS. if we want to make a coumn unique and not null then the column is defined as primary key. it is used to create relations among the tables. For any further detail, please visit the following links:http://www.iyogibusiness.com
What is difference between primary key and foreign key?
A primary key is an attribute (or combination of attributes) that uniquely identifies each row in a relation. A primary key is designated by underlining the attribute name. The primary key of an entity set allows us to distinguish among the various entities of the set. A foreign key is an attribute in a relation of database that serves as the primary key of another relation in the same database.
What is candidate key in dbms?
more than one primary key to identify the record uniquely is called candidate key.
Why do we designate one of the candidate keys of a relation to be the primary key?
A primary key is designated from among the candidate keys of a relation to uniquely identify each record in that relation and to ensure data integrity. It serves as a reference point for establishing relationships with other tables, facilitating efficient data retrieval and manipulation. Additionally, the primary key typically has constraints that prevent null values and duplicates, reinforcing the uniqueness of each entry in the database.
Entity integrity constraint?
The entity integrity constraint states that no primary key value can be null. This is because the primary key value is used to identify individual tuples in a relation. Having null value for the primary key implies that we cannot identify some tuples. This also specifies that there may not be any duplicate entries in primary key column key row.
Why do we designate one of the candidate keys of a relation be the primary key?
A primary key is designated from one of the candidate keys to uniquely identify each record in a relation, ensuring data integrity and preventing duplicate entries. It serves as a reference point for establishing relationships between tables in a database. Additionally, the primary key is typically optimized for performance, as it is often indexed, facilitating efficient data retrieval. Choosing a primary key also simplifies database design and enhances clarity in data management.
Explain two rules in relational model of database systems?
1) Entity Integrity: In a base relation, no attribute of a primary key can be null. 2) Referential Integrity: If foreign key exists in a relation, either foreign key value must match a candidate key value of some tuple in its home relation or foreign key value must be wholly null
What is the difference between Primarey key and Forn Key?
establishing a relation between two tables called fornkey.......the colum name should be unique is called "primary key"...a table contain only one primary key...a table contain more then one fornkey....
Which field MS Access will not allow you to delete?
A primary key field.A primary key field.A primary key field.A primary key field.A primary key field.A primary key field.A primary key field.A primary key field.A primary key field.A primary key field.A primary key field.
