Tag : pl/pgsql

pgSQL vs T-SQL – Enforce uniqueness on a column but allow multiple nulls

A Unique constraint is used to enforce unique values across one or many columns, often applied against Alternate keys of a table. Sometimes you want uniqueness enforced only where data for a column is present, and not where values are Null, for example, when storing optional Person attributes such as National Insurance numbers or Driving Licence numbers. Section 5.3.3. Unique…