table 1. SQL analog of either a relation or a relvar, as the context demands. Here are some of the major differences between tables in SQL and their relational counterparts: (a) SQL tables can contain duplicate rows; (b) SQL tables can contain nulls; (c) SQL tables have a left-to-right column sequence; (d) SQL tables can have two or more columns with the same name; (e) SQL tables can have what are, in effect, columns with no name at all. 2. More generally, a picture of a relation (on paper, for example). Note: Confusion between relations and such tabular pictures probably accounts for the popular misconception that relations are “flat” or two-dimensional. While it’ obviously true that those pictures are two-dimensional, relations in general aren't; rather, a relation of degree n is n-dimensional, in the sense that its tuples correspond to points in some n-dimensional space (one dimension for each attribute of the relation in question). One specific consequence of such considerations is that (again contrary to popular opinion) relations are perfectly capable of representing so called multidimensional data and thereby supporting so called online analytical processing (OLAP). See also cell; column; row.


Type Constraint Relational Calculus Extend Edition Online Analytical Processing Database Constraint 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

Copyright information

© C. J. Date 2008

Personalised recommendations