New posts in Unique Constraint

Why should a key be made explicit?

Email address unique or primary key?

Why does a UNIQUE constraint allow only one NULL?

Custom unique constraint, only enforced if one column has a specific value

Differences between "Unique Key" and "Primary Key"

PostgreSQL multi-column unique constraint and NULL values

When should I use a unique constraint instead of a unique index?

Add unique constraint to an existing PostgreSQL index

PostgreSQL: starting a sequence at MAX(the_column)+1

Add special constraint to avoid duplicate rows with this condition?