In PostgreSQL, we can ensure the relations stored inside a table a commutative-ly (or bidirectional etc) unique. For instance,

CREATE TABLE foo (   a int,   b int,   UNIQUE ( greatest(a,b), least(a,b) ) ); INSERT INTO foo VALUES (1,2); -- works INSERT INTO foo VALUES (2,1); -- explodes 

I know SQL Server can create computed columns, and using that I thought I could build what I want..

CREATE TABLE f (   a int,   b int,   g AS (CASE WHEN a>b THEN a ELSE b END),   l AS (CASE WHEN a>b THEN b ELSE a END),   UNIQUE(g,l) ); 

But I get, Msg 1934, Level 16, State 1, Server x230, Line 1

CREATE TABLE failed because the following SET options have incorrect settings: ‘QUOTED_IDENTIFIER’. Verify that SET options are correct for use with indexed views and/or indexes on computed columns and/or filtered indexes and/or query notifications and/or XML data type methods and/or spatial index operations.

Followed by, Msg 1750, Level 16, State 1, Server x230, Line 1

Could not create constraint or index. See previous errors.

So I guess that this can not be done with a UNIQUE index. Is this currently possible at all?