Add "Unique where not null" to create index
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Key: DERBY-2212
URL: https://issues.apache.org/jira/browse/DERBY-2212
Project: Derby
Issue Type: Improvement
Components: SQL
Affects Versions: 10.2.1.6
Reporter: Oleksandr Alesinskyy
Derby prohibits creation of unique constraints on nullable colums (as well if
only some columns in the constraint list are nullable) and treat nulls in
unique indexes as normal values (i.e. only one row with null values in indexed
columns may be inserted into the table). This bahavior is very restrictive,
does not completely comply with SQL standards (both letter and intent) as well
as with business needs and intending meaning of NULL values (2 null values are
not considered as equal, this comparision shall return NULL, and for selection
criteria boolean null is treated as FALSE).
This behavior, as far as I can see, is modelled after DB2 (and differs from
behavior of most other major databases, like SyBase, Oracle, etc.).
But even DB2 provide some means to alleviate these restrictions, namely "UNIQUE
WHERE NOT NULL" clause for CREATE INDEX statement.
It will be very good if such "UNIQUE WHERE NOT NULL" clause will be introduced
in Derby.
Regards,
Oleksandr Alesinskyy
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