unique value - trigger?

Hi folks,

I'm back with my lnumbers table again.

nymr=# \d lnumbers
Table "lnumbers"
Column | Type | Modifiers
-----------+-----------------------+-----------
lnid | integer | not null
lnumber | character varying(10) | not null
lncurrent | boolean |
Primary key: lnumbers_pkey
Triggers: RI_ConstraintTrigger_7575462

While each loco can have a number of different numbers, only one can be
current at any one time.

I want to make it so that if I set lncurrent to true for one row, any existing
true rows are set to false.

I'm guessing that I need to create a trigger to be actioned after an insert or
update which would update set lncurrent=false where lnid not = <current lnid>
but I can't seem to sus it put.

--
Gary Stainburn

This email does not contain private or confidential material as it
may be snooped on by interested government parties for unknown
and undisclosed purposes - Regulation of Investigatory Powers Act, 2000