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2963:SQL: Summarizing a Calculated Column

KEYWORDS: SQL DATABASE SUM CALCULATED AREA: Database Programming

Occasionally in a Delphi application that uses SQL to access data, it
becomes necessary to summarize calculated data. That is, to create a
calculated column and apply the SUM function to it.

When performing this operation against SQL tables (such as those for the
Local InterBase Server), it is a simple matter of enclosing the
calculation within the SUM function. For example, using the sample table
EMPLOYEE (in the EMPLOYEE.GDB database):

  SELECT SUM(SALARY / 12)
  FROM EMPLOYEE

This same methodology can also be used when the returned data set is to be
grouped by the value in another column with a GROUP BY clause:

  SELECT EMP_NO, SUM(SALARY / 12)
  FROM EMPLOYEE
  GROUP BY EMP_NO
  ORDER BY EMP_NO

While SQL databases support the summarization of calculated columns,
local SQL will not. Other means would be needed to obtain the results,
such as copying the results of a query with a calculated column to a
temporary table (as with a TBatchMove component) and then using a TQuery
component to summarize the data in the temporary table.


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