Get a count of unique column values in table

[rebelfox]

I have a feeling this will be very simple but by throbbing head can't think how to do this.

I have a Table Box with many rows that is effectively order detail lines.

Each row has an order number and a position number.

The position number is not always 1,2,3,4,5.  It can be 3,6,8,9,10 for example.

How can I get dynamically display in a separate statistics or text box the number of distinct order numbers selected in the Table Box?

[sunny_talwar · Accepted solution]

May be this in a text box object

Count(DISTINCT [order number])