A relational database, based on the relational model, allows the definition of data structures, storage and retrieval operations, and integrity constraints.
In such a database the data and relations between them are organized in tables.
A table is a collection of records and each record in a table contains the same fields. Certain fields may be designated as keys, which means that searches for specific values of that field will use indexing to speed them up.
book
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first_author
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title
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123
C. J. Date
n
Introduction to DB Systems
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234
Kenneth Jones
y
Algorithms
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345
Arthur King
n
Operating Systems
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...
...
...
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reader
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name
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224
Peter Stallings
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347
Laura Louden
...
...
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123
225
07-22-21
234
347
08-02-21
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Where fields in two different tables take values from the same set, a join operation can be performed to select records in the two tables by matching values in those fields.
Two unique features offered by relational systems are
Data independence
A condition that exists when data access is unaffected by changes in the physical data storage characteristics
SQL (Structured Query Language)
SQL is a relational database standard data-access language.
Nonprocedural processing means that the tables of a relational database can be manipulated in their entirety by special operators; there is no need to iterate tuple by tuple through the relation.