Base Tables and Related Elements
There was only one data structure in SQL; the table. Later standards and vendors added other structures, but they are almost never used and do not port. Tables have different flavors, but they all behave the same way. Conceptually, a table is a set of zero or more rows, and a row is a set of one or more columns. Each column has a specific data type and constraints that make up an implementation of an abstract domain for the values of the attribute modeled by the column. The way a table is physically implemented does not matter, because you access it only with SQL using a key. The database engine handles all the details for you and you never worry about the internals as you would with a physical file. In fact, ...
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