Add the 3 fields from the first table, then click Query > Append Query, then add the same 3 fields in the same order from the second table, then add the same 3 fields in the same order from the third table. This creates a UNION between the three tables; which means they need to be in the same order and have the same datatype.
If you want to show duplicate data found in the different sources, just change the UNION operator to a UNION ALL operator, otherwise it will suppress any duplicate rows.
To limit the data to one specific customer ID, you can set a limit on each of the UNION tabs with 'Customer ID = <selection>'.
..exactly what Jarod said, but let me add one thing...
The filters are processed before the OnPreProcess event occurs. If you make the limit in the first query variable you can add script to the OnPreProcess event to use the resulting value(s) to set the other two limits. That way you won't be asked for the same thing three times.