Minus

The Minus operator subtracts one stream from another stream. The order of subtraction is determined by the order in which you connect the input relations. You cannot subtract unlike operator attributes. The input schemas must be identical, with identical names and types for all attributes.

Specify the operator to subtract from, then choose the expression in the Expression drop-down list, where you can change the order for the subtraction operation. As with other operators, you can specify multiple input streams to a minus operation, and provide filters before the Minus operator.

To Create a Minus Operator

1. Drag a Minus operator from the Palette to the Design view.

2. Connect two or more input relations to the Minus operator.

3. Double-click the Minus operator.

   The Expression field provides the order of the minus expression. This is initially determined by the order in which the inputs were connected. You can determine this by opening the properties pane for the Minus operator. The input ID list provides the order of the operators that the Minus operator subtracts. Next, open the properties pane for the relations feeding into the Minus operator and examine their ID.

4. To change the order in the Expression dialog box, choose the Order by drop-down list and a new primary operator. The latter becomes the first operator on the Expression field. You can connect additional inputs to the Minus operator at a later time. You can also remove inputs. When you remove inputs, the Expression is automatically updated.