Relational keys
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Keys in relational databases uniquely identify tuples and include: - Super keys which uniquely identify tuples but may include unnecessary attributes. The relation Branch uses branch as a super key. - Candidate keys which uniquely identify tuples using only necessary attributes, like branchNo and postcode in the Branch relation. - Primary keys which are selected candidate keys like branchNo in the Branch relation. A primary key uniquely identifies tuples and cannot contain null values. - Alternate keys which are candidate keys not selected as primary keys, like postcode in the Branch relation. - Composite primary keys which use multiple attributes for unique identification, like Branch uses branchNo and postcode. - Foreign keys which match the primary key of another
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3) Candidate keys are attributes that qualify as primary keys and are minimal super keys. Alternate keys are other candidate keys besides the primary key.
Keys in Database
Keys in a database help uniquely identify rows. Super keys can identify rows but may contain redundant attributes, while candidate keys are minimal sets of attributes that uniquely identify rows. The primary key is the chosen candidate key that uniquely identifies each row; foreign keys in one table refer to the primary key of another table to link the tables.
key (1).pptx
The document defines and describes different types of keys used in database management systems. It explains that a primary key uniquely identifies each row in a table and cannot contain null values or duplicate values. A candidate key can also uniquely identify rows but other attributes can also qualify. An alternate key is like a primary key but a table can only have one primary key while other candidate keys are alternate keys. A composite key contains two or more columns that together uniquely identify each row. A super key can identify rows but may contain extra attributes, allowing null values. A foreign key points to the primary key in another table to link the tables.
Relational model
The document discusses the relational database model. It was introduced in 1970 and became popular due to its simplicity and mathematical foundation. The model represents data as relations (tables) with rows (tuples) and columns (attributes). Keys such as primary keys and foreign keys help define relationships between tables and enforce integrity constraints. The relational model provides a standardized way of structuring data through its use of relations, attributes, tuples and keys.
Free video lectures for mca
This document provides an overview of the key concepts in entity-relationship modeling including the three main elements - entity sets, attributes, and relationships. It defines these elements and provides examples like entities for departments, professors, students. It also describes other ER modeling concepts such as keys, single and multi-valued attributes, mapping cardinalities, participation constraints, weak entity sets, and identifying weak entity types. The document is presented as a lecture on ER modeling with examples to illustrate each concept.
Ch 6 Logical D B Design
The document discusses logical database design and the relational model. It defines key concepts like relations, attributes, keys, and integrity constraints. It also covers how to map an entity-relationship diagram to a set of normalized relational tables by decomposing relations to eliminate anomalies. The goal of normalization is to avoid data duplication and inconsistencies through transformations like removing partial and transitive dependencies.
FD.pdf
1. The document discusses different types of keys used in relational databases such as primary keys, candidate keys, foreign keys, and super keys. Primary keys uniquely identify each record in a table while foreign keys link two tables through a primary-foreign key relationship.
2. The document also covers database normalization forms including 1NF, 2NF, 3NF, BCNF, and 4NF which are used to organize data to reduce redundancy and inconsistencies. The normalization process divides tables and links them to eliminate anomalies like insertion, deletion, and modification anomalies.
3. Functional dependencies define relationships between attributes where non-key attributes depend on primary keys. Normalization aims to structure tables so that functional dependencies are preserved as
Database keys
Database keys are used to establish relationships between tables in a relational database and uniquely identify records. There are several types of keys: super keys identify tuples within a relation using one or more attributes; candidate keys are minimal super keys; the primary key is the candidate key chosen to uniquely identify tuples; alternate keys are other candidate keys not used as the primary key; a composite key is a primary key formed from multiple attributes; and a foreign key in one table references the primary key in another table to link the tables.
Keys.pptx
Keys play an important role in relational databases by uniquely identifying rows and establishing relationships between tables. There are several types of keys including primary keys, super keys, candidate keys, alternate keys, foreign keys, compound keys, and composite keys. A primary key uniquely identifies each row in a table and cannot be null, while other keys like alternate and foreign keys link data between tables or can uniquely identify rows without being designated as the primary key.
Logical database design and the relational model(database)
The document discusses logical database design and the relational model, including transforming entity-relationship diagrams into relations through a process called normalization to eliminate data anomalies and achieve well-structured relations. It defines the relational data model, explains how to map entities and relationships to tables, and covers the three normal forms to validate and improve table structure through analysis of functional dependencies between attributes.
Dbms keys
The document discusses different types of keys used in database management systems. It defines primary keys as columns that uniquely identify rows in a table and cannot contain null values. It also describes candidate keys, super keys, foreign keys, alternate keys, composite keys, and surrogate keys. The key types allow tables to be linked together and ensure uniqueness and integrity of data in the tables.
Database Keys
A key is a field or set of fields that uniquely identifies each record in a table. A candidate key is a field or set of fields that could serve as the primary key. The primary key is the candidate key that is chosen to uniquely identify each record. When no single field can uniquely identify records, a compound key that combines multiple fields can be used. A surrogate key is a unique identifier created specifically to identify records when the natural candidate keys do not adequately distinguish between records. Foreign keys are used to link records between tables based on matching primary key values.
DBMS-Keys , Attributes and Constraints.pptx
keys uniquely identify records;Attributes represent data characteristics, classified as simple or composite, with associated data types. Constraints maintain data integrity
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Logical database design and the relational model(database)
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Relational keys
- 1. Name: Sana Salah_ud_din M.Sc CS (final) Roll#: 138005 Topic: Keys In Relational Database
- 2. AT A Glance: Ø What is : Ø A Key ? Ø A Super Key ? Ø A Candidate Key ? Ø A Primary Key ? Ø An Alternate Key ? Ø
- 3. relational Key: A KEY is an attribute or set of attributes that uniquely identifies a TUPLE in a relation. There are two main types of key: A Super Key and a Foreign key Relational Keys Super Key Foreign Key Candidate Key Primary Key Alternate key Candidate Key
- 4. Super Key: An attribute, or set of attributes, that uniquely identifies a tuple within a relation. A Super key may contain additional attributes that are not necessary for unique identification. A super key is the most general type of key. EXAMPLE: As shown in the figure the relat- ion Branch has a super key
- 5. Candidate key: A key which is the candidate for being selected as a primary key. A candidate key contains only the attributes which can uniquely identify a tuple in a relation. As shown in the figure --- in the relation Branch the attributes branchNo & postcode can serve as candidate keys because both can uniquely identify a tuple in
- 6. Primary key: The candidate key that is selected to identify tuples uniquely within the relation. Some most important points about primary key are: A relation can have only one primary key. Each value in primary key attribute must be unique. Primary key cannot contain null values. As shown in the figure---- the attribute branchNo can serve as primary key because
- 7. Alternate key: The candidate keys that are not selected as primary key are known as alternate keys. As shown in the figure the relation Branch has branchNo serving as pri- mary key and postcode serving as alternate key because postcode can
- 8. Composite Key: A primary key that consists of two or more attributes is known as COMPOSITE KEY. As shown in the figu- re– the relation Branch has two attributes serving as primary key so this is a composite key,
- 9. Foreign key: An attribute, or set of attributes, within one relation that matches the candidate key of some relation.. As shown in the figur- e in the relation Staff The attribute branchNo is the foreign key because it is the prim- ary key in the relation Branch.
- 10. The end
Editor's Notes
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