March 14th, 2010
Base Table, Part 2 of 2
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B. SQL Basics
> All data is represented by values.
> Each column has a single value for each row. An alternative is to have a NULL value, which means that there is no value (not even blank).
> The order of rows (left to right) and columns (top to bottom) is unimportant.
> Unique identification of each row by a column (or columns) is called a Primary Key.
> Relationships to other tables exist as values in a column (or columns) and are called Foreign Keys.
> No duplicate rows are allowed (duplicate data across all Primary Key columns).
> No duplicate columns are allowed. (If you have multiple addresses, use ADDR1, ADDR2, ADDR3, not ADDR, ADDR, ADDR)
