2 "-~ O C H A P T E R I 0 Simple Data Rule Analysis
RULES INVOLVING MULTIPLE ROWS OF SAME COLUMN
The rules shown so far involve values contained in a single row. Sometimes an
object has multiple rows for parts of the data object. For example, an ORDER
has line item detail rows; a project has multiple people working on it. Rules
can apply to these that involve looking at more than one row at a time but still
within the boundaries of the single data object.
An example is testing for uniqueness across the P RODUCT_ID column
of ORDER_LINE_ITEMS. This is a column that is not unique across the
entire
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