Re: unique constraint definition within create table

On Tue, Dec 1, 2015 at 11:36 PM, Andreas Kretschmer <
akretschmer(at)spamfence(dot)net> wrote:

> Hi @ll,
>
> 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?
>

​You might consider adding a table constraint "u1 <= u2"​. You could also
consider adding a trigger that munges data on INSERT/UPDATE so that this
constraint is met regardless of the order supplied by the user.

David J.