PostgreSQL: default constraint names

When creating a table in PostgreSQL, default constraint names will assigned if not provided:

CREATE TABLE example (
    a integer,
    b integer,
    UNIQUE (a, b)
);

But using ALTER TABLE to add a constraint it seems a name is mandatory:

ALTER TABLE example ADD CONSTRAINT my_explicit_constraint_name UNIQUE (a, b);

This has caused some naming inconsistencies on projects I've worked on, and prompts the following questions:

1. Is there a simple way to add a constraint to an extant table with the name it would have received if added during table creation?

2. If not, should default names be avoided altogether to prevent inconsistencies?

The standard names for indexes in PostgreSQL are:

{tablename}_{columnname(s)}_{suffix}

where the suffix is one of the following:

• pkey for a Primary Key constraint
• key for a Unique constraint
• excl for an Exclusion constraint
• idx for any other kind of index
• fkey for a Foreign key
• check for a Check constraint

Standard suffix for sequences is

• seq for all sequences

Proof of your UNIQUE-constraint: > NOTICE: CREATE TABLE / UNIQUE will > create implicit index > "example_a_b_key" for table "example"

The manual is pretty clear about this ("tableconstraint: This form adds a new constraint to a table using the same syntax as CREATE TABLE.")

So you can simply run:

ALTER TABLE example ADD UNIQUE (a, b);