Providing a unique key for a table
Use ROWID columns or identity columns to store unique values for each row in a table.
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Question: How can I provide a unique identifier for a table that has no unique column?
Answer: Add a column with the data type ROWID or an identity column. ROWID columns and identity columns contain a unique value for each row in the table. You can define the column as GENERATED ALWAYS, which means that you cannot insert values into the column, or GENERATED BY DEFAULT, which means that DB2® generates a value if you do not specify one. If you define the ROWID or identity column as GENERATED BY DEFAULT, you need to define a unique index that includes only that column to guarantee uniqueness.