Unity overrides certain non-deterministic functions, such as current time and random. The following table shows which SQL functions are automatically rewritten if used in a SQL request which performs a write.
| SQL Function | Replacement |
|---|---|
| RANDOM | If CDM is disabled, active sequencer replaces this function with a single randomly generated value. A single write request involving multiple rows results in the same random number. If CDM is enabled, Unity does not replace the RANDOM clause. The write requests are replicated using CDM. |
| CURRENT_DATE | Active sequencer generates a date to replace this function. |
| CURRENT_TIME | Active sequencer generates a time to replace this function. |
| CURRENT_TIMESTAMP | Active sequencer generates a timestamp to replace this function. |
| DATE | Active sequencer generates a date to replace this function. |
| SESSION | Not supported. |
| TIME | Active sequencer generates a time to replace this function. |
| HASHAMP | Not supported. |
| HASHBAKAMP | Not supported. |
| HASHROW | Not supported. |
| HASHBUCKET | Not supported. |
| ROW NUMBER | If CDM is disabled, not supported. If CDM is enabled, write replicated using CDM. |
| Sample Clause | If CDM is disabled, not supported. If CDM is enabled, write requests using SAMPLE clause are supported and replicated using CDM. |
| INSERT into table with identity column | If CDM is disabled, not supported. If CDM is enabled, write replicated using CDM. |
| Non-deterministic User-Defined Function | If CDM is disabled, write replicated using SQL Multicast. If CDM is enabled, write replicated using CDM. |
| Stored procedure call | If CDM is disabled, writes are replicated using SQL Multicast. Traditional Unity SP limitations apply. If CDM is enabled, writes are replicated using the enhanced stored procedure feature. Traditional limitations do not apply. |
| Write using READ_NOS table operator | If CDM is disabled, not supported. If CDM is enabled, write replicated using CDM. |
| Write using foreign tables | If CDM is disabled, not supported. If CDM is enabled, write replicated using CDM. |
| Updatable Cursors | If CDM is disabled, write replication is not supported. If CDM is enabled, writes are replicated using CDM. |
Unity must be part of the secure database cluster to verify override. The secure database cluster includes Unity and all Teradata systems it manages. Systems in the secure database cluster are identified through shared proxy certificates that must exist on all database nodes and on all Unity server nodes.
For more information on Teradata Proxy certificates, see Teradata Vantage™ - Advanced SQL Engine Security Administration, B035-1100.