default: nulls distinct

BigQueryDb2 (LUW)MariaDBMySQLOracle DBPostgreSQLSQL ServerSQLite200520072009201120132015201720192021✓ 3.5.7+⊘ 2008R2 - 2019✓ 8.3+⚠ 11gR1 - 21cb✓ 5.0+✓ 5.1+
  1. Doesn’t support null-able columns in unique constraints (T591)
  2. If all constraint columns are null