Re: unique constraint definition within create table

Andreas Kretschmer <akretschmer@spamfence.net> writes:
> i'm trying to create a table with 2 int-columns and a constraint that a
> pair of (x,y) cannot be as (y,x) inserted:

> test=# create table foo(u1 int,u2 int, unique (least(u1,u2),greatest(u1,u2)));
> ERROR:  syntax error at or near "("
> LINE 1: create table foo(u1 int,u2 int, unique (least(u1,u2),greates...

> I know, i can solve that in this way:

> test=*# create table foo(u1 int,u2 int);
> CREATE TABLE
> test=*# create unique index idx_foo on foo(least(u1,u2),greatest(u1,u2));
> CREATE INDEX

> But is there a way to define the unique constraint within the create table - command?

No.  Per SQL standard, the argument of a UNIQUE (or PRIMARY KEY)
constraint can only be a list of column names.

We would consider relaxing that, except it would break the
information_schema views for such constraints.
        regards, tom lane