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What does the word "Relational" mean here? Is it tables being related to each other just like the real life entities, or does it mean something else?

  • 4
    That's, btw, the most common misconception about RDBMSes I hear. – vartec Apr 20 '11 at 7:49
  • @vartec: Is it the part I said about "relating to real life entities"? – Shamim Hafiz Apr 20 '11 at 8:13
  • The part "tables being related to each". – vartec Apr 20 '11 at 8:28
  • I think it's that every table defines a series of relationships within itself. – Erik Reppen May 27 '17 at 3:46

From Wikipedia:

A relational database matches data by using common characteristics found within the data set. The resulting groups of data are organized and are much easier for many people to understand.

and further down:

A relation is defined as a set of tuples that have the same attributes. A tuple usually represents an object and information about that object. Objects are typically physical objects or concepts. A relation is usually described as a table, which is organized into rows and columns. All the data referenced by an attribute are in the same domain and conform to the same constraints.

The tables are related to each other by common attributes that can then be used to form more complex queries for pulling data.

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The word relational comes from http://en.wikipedia.org/wiki/Relational_algebra which was invented by E.F. Codd. SQL and relational databases started as an attempt to make Codd's ideas practical.

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  • IIRC Codd based his ideas on the relational theory branch of mathematics. My DB theory classes were too long ago to remember where/when relational theory came from. Maybe some visitors from cstheory.stackexchange can correct me. – jqa Mar 28 '12 at 1:48

A relation is a table in database context.

A relation is a data structure which consists of a heading and an unordered set of tuples which share the same type. --Wikipedia

It's more about how the data is related to the column name and type than how keys are related to foreign-keys.

For example, a data set containing all the real-estate transactions in a town can be grouped by the year each transaction occurred, the sale price, a buyer's last name and so on. Such a grouping uses the relational model (a technical term for this is schema). Hence, such a database is called a "relational database." --Wikipedia

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