table1 
ID    |   City  |State
469	HARVEY   	IL
470	HARTVILLE	OH
471	HARRISON	OH
472	HARLEYSVILLE	PA
473	HAMMOND         IN
474	HAMILTON	ON
475	HAMILTON	ON
476	HAMILTON	OH
477	HALIFAX  	NS
478	GUELPH  	ON
479	GROVEPORT	OH
480	GROVE CITY	OH
481	GREENVILLE	OH
482	GREENVILLE	OH
483	GREENVILLE	PA

table2

ZipCode|City           |State
12138	North Petersburg	NY
12138	Petersburg	NY
12138	Petersburgh	NY
12138	Taconic Lake	NY
12139	Arietta 	NY
12139	Piseco	        NY
12140	Poestenkill	NY
12141	Quaker Street	NY
12143	Ravena       	NY
12144	Defreestville	NY
12144	Rensselaer	NY
12147	Rensselaerville	NY
12147	Rensselaervle	NY
12148	Rexford 	NY
12148	Vischer Ferry	NY
12149	Richmondville	NY
12149	West Richmondville	NY
12150	Rotterdam Jct	NY
12150	Rotterdam Junction	NY

quote:

---

Originally posted by webfred

Can you please give sample data that is fitting your requirements?

---

Sorry maybe im not clear.

update table1 where t1.city = t2.city AND t1.state=t2.state AND there is only 1 count of that city in t2

Table1(customerData)
ID | city   |    state | zip
3  greenville   OH     NULL
4 Dublin         OH      NULL


Table2 (zipCodeLookup)

greenville      OH      04452
Alexandria	OH	43001
Amlin   	OH	43002
Ashley   	OH	43003
Blacklick	OH	43004
Bladensburg	OH	43005
Brinkhaven	OH	43006
Broadway	OH	43007
Buckeye Lake	OH	43008
Cable   	OH	43009
Catawba   	OH	43010
Centerburg	OH	43011
Croton  	OH	43013
Danville	OH	43014
Delaware	OH	43015
Dublin  	OH	43016
Dublin  	OH	43017
Etna    	OH	43018
Fredericktown	OH	43019
Fredricktwn	OH	43019
Galena  	OH	43021


Update table1 
with zipcode from table2 where t1.city=t2.city & t1.state=t2.state & count(t2.city) = 1

Result
-------
id  city   state   zipcode
3   Greensville  OH   04452
4   Dublin       OH   NULL   --Because it had 2 zips for same city

declare @r table (id int,city varchar(40), [state] varchar(2), zip varchar(5))
insert @r
select 3,'greenville','OH',null union all
select 4,'Dublin','OH',null union all
select 5,'Etna','OH',null 

declare @t table (city varchar(40), [state] varchar(2), zip varchar(5))
insert @t
select 'greenville',      'OH',      '04452' union all
select 'Alexandria',	'OH',	'43001' union all
select 'Dublin',  	'OH',	'43016' union all
select 'Dublin',  	'OH',	'43017' union all
select 'Etna',    	'OH',	'43018'

update a
set a.zip = b.zip
from @r a inner join 
(select city,max(zip) as zip,max([state]) as [state]
from @t group by city
having count(city) = 1
) b 
on a.city = b.city and a.state = b.state

id          city                                     state zip
----------- ---------------------------------------- ----- -----
3           greenville                               OH    04452
4           Dublin                                   OH    NULL
5           Etna                                     OH    43018