In a heap structure, the table has no key--it is simply a heap of data. When you add a row, it is added to the end of the heap. This makes heap the fastest storage structure to use when you are initially loading tables or adding a large quantity of data.

However, when you want to retrieve a particular row from a heap table, you must search through every row in the table looking for rows that qualify. This makes heap relatively slow for retrieval if tables have more than a few pages. For more information, see the chapter “Maintaining Storage Structures.”