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

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

Related

• Implementation-defined

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

• Optional features

  • T591, "UNIQUE constraints of possibly null columns"

• Tutorials:

  • NULL: Indicating the Absence of Data

Normative References

The implementation defined item IA201, "Whether two rows whose column values are all the null value are considered unique with nulls distinct, or unique with nulls not distinct" is defined in ISO/IEC 9075-2:2023. It first appeared in 2023. Previously, nulls distinct was the standard behavior.

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