null
-able columns in unique constraints (T591)The default null treatment of unique constraints is implementation defined. Note that nulls not distinct
unique constraints may still treat null
values as distinct from each other for rows where all constraint columns are null
.0
null
-able columns in unique constraints (T591)null
null
The optional feature F292, “UNIQUE null treatment” is in a draft for the upcoming SQL standard.
Note that SQL:2016 specifies the behaviour of nulls distinct
as the only way to cope with null
values in unique constraints. In the mentioned draft the default behaviour is implementation defined.
The essence of SQL tuning in 200 pages
Buy now!
(paperback and/or PDF)
Paperback also available at Amazon.com.
Markus offers SQL training and consulting for developers working at companies of any size.
Learn more »
CD 9075-2:202x(E), 4.25.3.2 Unique constraints (in particular NOTE 52).