default:
nulls not distinct
BigQuery
Db2 (LUW)
MariaDB
MySQL
Oracle DB
PostgreSQL
SQL Server
SQLite
2005
2007
2009
2011
2013
2015
2017
2019
2021
⊘ 3.5.7 - 3.41.0
✓ 2008R2+
⊘ 8.3 - 15
⚠ 11gR1 - 21c
a
⊘ 5.0 - 8.0.32
⊘ 5.1 - 10.11
If some but not all constraint columns are
null
Doesn’t support
null
-able columns in unique constraints (T591)