A unique key is a set of one or more than one fields/columns of a table that uniquely identify a record in a database table. You can say that it is little like primary key but it can accept only one null value and it cannot have duplicate values.
For instance user wants to select unique key for base table LINEITEM and columns L_ORDERKEY , L_PARTKEY.
To create unique key in uArrow:
Click on tick the box for columns L_ORDERKEY , L_PARTKEY columns for unique key.