Specify the start position within the Substring from Column.
There is no requirement for an end position as this is automatically calculated by adding the length of the virtual column to the start position. (Refer to 3.3.1 Virtual Column Name.)
Value must be less than the length of the Substring from Column.
The length of the Substring from Column minus the value of the Start Position must not be greater than the virtual column nominated in the 3.3.1 Virtual Column Name (unless *RECORD has been specified), i.e. the length of the substring data must fit into the virtual column.