Re: Making a unique constraint deferrable?

["David G. Johnston" <david.g.johnston@xxxxxxxxx>]

On Tue, Feb 28, 2017 at 10:05 AM, Ivan Voras <ivoras@xxxxxxxxx> wrote:

On 28 February 2017 at 18:03, David G. Johnston <david.g.johnston@xxxxxxxxx> wrote:

On Tue, Feb 28, 2017 at 9:50 AM, Ivan Voras <ivoras@xxxxxxxxx> wrote:

ivoras=# alter table foo alter constraint "foo_a_b_key" deferrable;

ERROR:  constraint "foo_a_b_key" of relation "foo" is not a foreign key constraint

​A more clear error message would be:

EROR:  cannot alter non-foreign key constraint "foo_a_b_key"​ of relation "foo"

Though I'm not sure how that meshes with the error message style guides...

Any idea what underlying technical reason prohibits marking non-fk constraints as deferrable?

Not off hand - but a unique (and PK by extension) constraint is implemented by creating an underlying unique index​ and the ALTER CONSTRAINT command probably doesn't want to go messing around with that.  While the columns involved in a FK constraint can also be indexed the two concepts are not physically linked together.

David J.