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UNIQUE WHERE NOT NULL indexes

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Some of you may know that I am engaged in enabling Oracle applications to DB2. One of the frequent "issues" we see are differences between the way how indexing works in Oracle and DB2 and, more specifically about different semantics for unique indexes. In DB2 a unique index requires that no two keys are the same. Sounds simple and clear on the surface, but not so clear when you consider NULLs. Generally speaking a NULL cannot be compared to a NULL and thus it is debatable whether one should allow more than one NULL key in a unique... [More]

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UNIQUE WHERE NOT NULL indexes