ID106 - The unique null treatment when no explicit unique null treatment is specified

UNIQUE NULLS [NOT] DISTINCT (...)

1. Doesn’t support null-able columns in unique constraints (T591)

Related

• Implementation-defined

  • IA201 - Whether two rows whose column values are all the null value are considered unique with nulls distinct, or unique with nulls not distinct

• Optional features

  • T591, "UNIQUE constraints of possibly null columns"

• Tutorials:

  • NULL: Indicating the Absence of Data

Normative References

The implementation defined item ID106, "The unique null treatment when no explicit unique null treatment is specified" is defined in ISO/IEC 9075-2:2023. It first appeared in 2023. Previously, nulls distinct was the standard behavior.

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