Identity Columns and Bulk Inserts
Identity column values for rows bulk-inserted into a table defined with a GENERATED ALWAYS identity column are replaced automatically with system‑generated numbers. A warning of this replacement is issued only once for all rows inserted using an INSERT ... SELECT request. Other bulk‑inserting utilities such as Teradata Parallel Data Pump and BTEQ imports receive the same warning for each row inserted.
Rows bulk‑inserted into tables with either of the following identity column definitions are not guaranteed to be unique unless the appropriate row columns are constrained by a UPI, USI, PRIMARY KEY, or UNIQUE constraint.