A placeholder is a column for which you set the datatype and value in PL/SQL that you define. Placeholder columns are useful when you want to selectively set the value of a column (for example, each time the nth record is fetched, or each time a record containing a specific value is fetched, and so on). You can set the value of a placeholder column in the following places:
the Before Report Trigger, if the placeholder is a report-level column
a report-level formula column, if the placeholder is a report-level column
a formula in the placeholder's group or a group below it (the value is set once for each record of the group)
Creating or editing a placeholder column
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