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Summary Unit 2 Creating system to manage information Keywords
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it for unit 2 and its about the definitions of the keywords.
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Name: Sabiha ChoudhuryBMC171817858
Unit 2 Creating systems to manage information
Classwork Homework
Primary Key
Primary keys (columns) in a table are a minimal set of attributes that uniquely identify each
tuple (row) in the table. The database designer can select any of the candidates as the
primary key on a table if it contains one primary key.
Table rows should all have unique values for the primary key.
The primary key of a table is usually one of the fields, which can either be a number
or another data type.
One of the main attributes of a primary key is that it must contain a unique value
for each row of data and null values are not permitted.
Foreign Key
In a relational database table, a foreign key is a column or field that links records in two
different tables. It does this by referencing the primary key of one table and accessing it
through another table. For foreign keys to function, two tables need to be given a
relationship.
Candidate Key
Candidate keys are the fields that contribute most to uniquely identifying a tuple.
Candidates keys refer to the fields from which the primary key can be selected. In SQL,
candidate keys may contain multiple attributes. The main purpose of the candidate is to
offer multiple options to the database designers so that suitable primary key can be
selected.
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