Dataset as the name implies it is set of data that are result of the query that is set in the query area of the dataset configuration. In certain times we can’t able to resist creating multiple datasets in a single report. Once such case is using D365 FetchXML datasets, the limitation causes the reason for multiple datasets.
Dealing with multiple dataset is straightforward if they are mapped to different Tablix. As one Tablix can able to reference one dataset. But, when you want have one Tablix and want to refer multiple datasets values there arise the problem. In these cases, SSRS comes to rescue and handle it using the lookup function.
Below is the simple way you can able to reference multiple dataset in a single Tablix.
Lookup(Fields!ID.Value,Fields!ID.Value,Fields!DataSet_1_Field.Value,"DataSet2Name")
In the above formula, the first argument is the ID of the main dataset that is referenced in the Tablix, the second argument is the ID of the dataset that you want to use, the third argument is the field that you want to show in the Tablix column, the final and the fourth argument is the dataset name that you want to use.
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