Allow unique constraints to pass if one of the columns is null
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Key: DERBY-653
URL: http://issues.apache.org/jira/browse/DERBY-653
Project: Derby
Type: Bug
Components: SQL
Reporter: Rick Hillegas
This appears to be the behavior required by ansi. This issue was raised by Dan
Meany on the user list in a thread titled "Unique constraints on multiple
fields with one nullable" on October 26, 2005. Sybase and Postgres allow this
behavior. DB2 finesses the issue by not allowing you to declare a unique
constraint on nullable columns. Here is Dan's post:
I noticed that in Derby a unique constraint on two
columns A and B, with B nullable, will prevent
inserting two identical records that contain NULL in
B.
This is different from some other databases such as
Sybase that do allow it (I assume where the null
records are not in stored as part of the unique
index).
I noticed this while transfering data from Sybase to
Derby using Apache dbutils and getting rejected
duplicate records.
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