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Chapter 10. Creating Multitable and Cros... > Making Calculations on Multiple Reco...

Making Calculations on Multiple Records

One of SQL's most powerful capabilities is that of obtaining summary information almost instantly from specified sets of records in tables. Summarized information from databases is the basis for virtually all management information systems (MIS). These systems usually answer questions such as, What are our sales to date for this month? or How did last month's sales compare with the same month last year? To answer these questions, you must create queries that make calculations on field values from all or selected sets of records in a table. To make calculations on table values, you must create a query that uses the table and employ Access's SQL aggregate functions to perform the calculations.

Using the SQL Aggregate Functions

Summary calculations on fields of tables included in query result tables use the SQL aggregate functions listed in Table 10.1. These are called aggregate functions because they apply to groups (aggregations) of data cells. The SQL aggregate functions satisfy the requirements of most queries needed for business applications. You can write special user-defined functions with Access VBA code to apply more sophisticated statistical, scientific, or engineering aggregate functions to your data.


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