In terms of the
relational model of databases, a table can be considered a convenient representation of a
relation, but the two are not strictly equivalent. For instance, a
SQL table can potentially contain duplicate rows, whereas a true relation cannot contain duplicate rows that we call
tuples. Similarly, representation as a table implies a particular ordering to the rows and columns, whereas a relation is explicitly unordered. However, the database system does not guarantee any ordering of the rows unless an
ORDER BY clause is specified in the
SELECT statement that queries the table. An equally valid representation of a relation is as an
n-dimensional
chart, where
n is the number of attributes (a table's columns). For example, a relation with two attributes and three values can be represented as a table with two columns and three rows, or as a two-dimensional graph with three points. The table and graph representations are only equivalent if the ordering of rows is not significant, and the table has no duplicate rows. ==Comparisons==