How will you design the report where rows as well as the columns are not fixed?

For creating this report you can use Matrix report as for matrix report both rows and column can grow at run time.

Use a matrix to display grouped data and summary information. You can group data by multiple fields or expressions in row and column groups. Matrices provide functionality similar to crosstabs and pivot tables. At run time, as the report data and data regions are combined, a matrix grows horizontally and vertically on the page. Values in matrix cells display aggregate values scoped to the intersection of the row and column groups to which the cell belongs. You can format the rows and columns to highlight the data you want to emphasize. You can also include drilldown toggles that initially hide detail data; the user can then click the toggles to display more or less detail as needed.

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