A computed column
stores the results of computational tasks. For example, a computed
column can be used to convert unit measurements so that all the data
uses the same standardized units of measurement. You can add, modify,
or delete computed columns on the
Add or modify computed
columns page that is available in the
Summarized
Aggregation Table wizard or the
Simple Aggregation
Table wizard. By default, a computed column is numeric.
Note: If you change a computed
column, the values for the computed column are recalculated for that
column in all rows of the data when the job is executed. (This recalculation
is performed even if no new data is added to the aggregation table.)
The
Specify
computed columns page displays a grid that shows the
following fields for each computed column:
Name,
Expression,
Description,
Length,
Type,
Informat,
and
Format.
Tip
A computed column called
TimePeriod
is
automatically added to every simple and summarized aggregation table.
Its value is always the same as the aging column, and you can refer
to
TimePeriod
instead of referring
to the aging column directly. This technique simplifies reporting,
especially in those instances where you do not know the name of the
aging column. (If no aging is specified for the target table, then
the field is set to missing.) The expression for this column is defined
when the aggregation wizard is completed. For example, if the aging
column of an aggregation table is DAYDATE, the expression for the
TimePeriod computed column is DAYDATE and its expression is
TIMEPERIOD=DAYDATE;
.
On the
Specify
computed columns page, you can create, modify, or delete
computed columns.