Handle Non-Deterministic Elements | Teradata Unity - 17.00 - Handling of Non-Deterministic Elements - Continuous Availability - Teradata Unity

Teradata® Unity™ User Guide

Product
Continuous Availability
Teradata Unity
Release Number
17.00
Published
September 2020
Language
English (United States)
Last Update
2020-09-15
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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.