Relational Databases 101—Creating Tables, Rows, and Columns

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Creating Tables, Rows, and Columns

Relational databases are defined in fairly simple terms:

• Database: An extensible collection of related data typically organized as a set of tables. For example, an accounting database would contain information about the customers, inventory, orders, items, and other details of the accounting operation. Where and how the data is stored, protected, fetched, and updated is irrelevant, as it is managed entirely by the database management system (DBMS). The key word here is "extensible." Due to its fundamental design, a relational database is easily expanded to encompass more data entities to store.

• Tables: An extensible collection of rows containing related data. For example, the Customers table would contain a collection of rows pertaining to (just) customers—not the things they order, or sell, or where they bank—just about the individual customer.

• Rows: An extensible collection of column headings and typed columns to contain data details collected in a single table. Each row pertains to a single entity as a row in the Customers table would refer to a single customer. There is never an implied row order in a relational data table—this means, unless specifically requested, rows are returned in a nondeterministic order. This is especially true of SQL Server 2005 queries—with parallel processing, even rows stored with a clustered index can appear in any order.

• Columns: A named storage place for base-typed, user-defined typed, or (in the case of SQL Server) sql_variant "morphing" typed data. Columns are always returned in the order in which they are defined unless otherwise requested.