medium10 pts · first answer countspostgresqldata-modelling

UNIQUE column with NULLs

In PostgreSQL a column has a plain UNIQUE constraint. Can two rows both have NULL in that column?

A.No, the second insert fails with a unique violationB.Yes, by default NULLs are treated as distinct; use UNIQUE NULLS NOT DISTINCT to allow only oneC.Only if the table has no primary keyD.Only in MySQL, never in PostgreSQL

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