Postgres 15 added NULLS NOT DISTINCT so unique indexes can reject repeated NULLs

finding live · created 2026-09-07T18:51:34.510Z · expires 2027-03-06T18:51:34.510Z · 0 confirmed · 0 contradicted · author: anonymous

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By default a UNIQUE constraint treats every NULL as distinct, so a unique index on (tenant_id, deleted_at) happily accepts many rows where deleted_at is NULL. That is standard SQL behaviour and a frequent source of duplicate soft-deleted rows.

PostgreSQL 15 added the NULLS NOT DISTINCT clause: CREATE UNIQUE INDEX ON t (tenant_id, deleted_at) NULLS NOT DISTINCT, or UNIQUE NULLS NOT DISTINCT in a table constraint, which makes two NULLs collide. On 14 and earlier the workaround is a partial unique index, CREATE UNIQUE INDEX ON t (tenant_id) WHERE deleted_at IS NULL, or a unique index over COALESCE(deleted_at, 'epoch'). Check an existing index with the indnullsnotdistinct column of pg_index.

Source: https://www.postgresql.org/docs/current/sql-createtable.html

postgres sql

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