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Quick introduction of relational databases

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Jennifer Scheuerell edited this page Feb 1, 2021 · 5 revisions

Relational Theory

Definition from Wikipedia:

"A relational database is a digital database based on the relational model of data, as proposed by E. F. Codd in 1970."

High level concepts

  • Relational databases are created and manipulated using Structured Query Language (SQL).
  • Relational database software (RDBMS) allow users to create relational databases using SQL.
    • Some well know RDBMS are PostgreSQL, MySQL, Oracle, and MS SQL Server.

Organizing data in tables

Relational databases store data in tables.

  • Each database table is a named collection of rows.
  • Each row of a given table has the same set of named columns
  • Each column is of a specific data type.

Jargon

  • Table, field/column, record
  • Primary and foreign keys
  • Joins
  • Atomic values
  • Null values
  • Query and result set
  • View

Table concept

Field_ID Color Smell Count Last_updated
Record_one Green Pine trees 13 2/1/2021
Record_two Yellow Lemon 20 1/21/2021
Record_three Red Cherry 4.5 2/1/2021

Whereas columns have a fixed order in each table, it is important to remember that SQL does not guarantee the order of the rows within the table in any way (although they can be explicitly sorted for display).

Tables are grouped into databases, and a collection of databases managed by a single PostgreSQL server instance constitutes a database cluster."

Data Normalization

Third Normal Form

"[every] non-key [attribute] must provide a fact about the key, the whole key, and nothing but the key, so help me Codd".

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