How to create a case-insensitive unique constraint?

["Kynn Jones" <kynnjo@xxxxxxxxx>]

Hi!

If I try something like

ALTER TABLE foo

  ADD CONSTRAINT foo_unique_xy

  UNIQUE ( UPPER( x ), UPPER( y ) );

...I get a syntax error

ERROR:  syntax error at or near "("

LINE 3:   UNIQUE ( UPPER( x ), UPPER( y ) );

Is there a way to do this?

TIA!

Kynn