Sql query Postcode search using first 3 characters

Question

I'm doing a query to bring back all the email addresses of our clients that live in Scotland currently the postcode column has the full length postcode 'YO7 4LL'

Below is the query iv tried to use

SELECT cast(left(postcode) as varchar),email
from dbo.SubscriberList
WHERE Postcode  in (
'AB1','AB2','AB23','AB3','AB30','AB31','AB32','AB33','AB34','AB35','AB36','AB41',
'AB42','AB43','AB44','AB45','AB51','AB52','AB53','AB54','AB55','DD10','DD9',
'FK17','G82','G83','G84','PA20','PA21','PA22','PA23','PA24','PA25','PA26','PA27',
'PA28','PA29','PA30','PA31','PA32','PA33','PA34','PA35','PA36','PA37','PA38','PA41',
'PA42','PA43','PA44','PA45','PA46','PA47','PA48','PA49','PA60','PA61','PA62','PA63',
'PA64','PA65','PA66','PA67','PA68','PA70','PA71','PA72','PA73','PA74','PA75','PA76',
'PA77','PA78','DG7','KA1','KA10','KA11','KA12','KA13','KA14','KA15','KA16','KA17',
'KA18','KA19','KA2',
'KA20','KA21','KA22','KA23','KA24','KA25','KA26','KA27','KA28','KA29','KA3','KA30','KA4',
'KA5','KA6','KA7','KA8','KA9','PA17','FK10','FK11','FK12','FK13','FK14',
'DG1','DG10','DG11','DG12','DG13','DG14','DG16','DG2','DG3','DG4','DG5',
'DG6','DG7','DG8','DG9','KA6','ML12',
'G60','G61','G62','G64','G65','G66','G81','G82','G83','DD1','DD2','DD3','DD5',
'EH21','EH22','EH31','EH32','EH33','EH34','EH35','EH36','EH39','EH40',
'EH41','EH42','TD13','EH1','EH10','EH12','EH13','EH14','EH15','EH16','EH17',
'EH2','EH20','EH21','EH28','EH29','EH3','EH30','EH4','EH5','EH6','EH7','EH8','EH9',
'FK1','FK10','FK11','FK12','FK13','FK14','FK15','FK16','FK17','FK18','FK19','FK2',
'FK20','FK21','FK3','FK4','FK5','FK6','FK7','FK8','FK9',
'DD6','FK10','KY1','KY10','KY11','KY12','KY13','KY14','KY15','KY16','KY2',
'KY3','KY4','KY5','KY6','KY7','KY8','KY9',
'G1','G11','G12','G14','G15','G2','G20','G21','G32','G41','G43','G45','G51','G53','G76',
'AB37','IV1','IV10','IV11','IV12','IV13','IV14','IV15','IV16','IV17','IV18','IV19',
'IV2','IV20','IV21','IV22','IV23','IV24','IV25','IV26','IV27','IV28','IV3','IV4','IV40',
'IV41','IV42','IV43','IV44','IV45','IV46','IV47','IV48','IV49',
'IV5','IV51','IV52','IV53','IV54','IV55','IV56','IV6','IV7','IV8','IV9','KW1',
'KW10','KW11','KW12','KW13','KW14','KW2','KW3','KW5','KW6','KW7','KW8','KW9','PA34',
'PA38','PA39','PA40','PH19','PH20','PH21','PH22','PH23','PH24','PH25',
'PH26','PH30','PH31','PH32','PH33','PH34','PH35','PH36','PH37','PH38','PH39',
'PH40','PH41','PH42','PH43','PH44',
'PA10','PA11','PA13','PA14','PA16','PA18','PA19',
'EH46','EH55','G33','G65','G66','G67','G68','G69','G71','G72','G73','G74','G75','ML1',
'ML10','ML11','ML12','ML2','ML3','ML4','ML5','ML6','ML7','ML8','ML9',
'EH10','EH18','EH19','EH20','EH22','EH23','EH24','EH25','EH26','EH37','EH46',
'AB37','AB38','AB56','IV30','IV31','IV32','IV36','PH26',
'KW1','KW15','KW16','KW17',
'DD2','FK14','FK15','FK19','FK21','KY13','PH1','PH10','PH11','PH12','PH13','PH14','PH15',
'PH16','PH17','PH18','PH2','PH3','PH4','PH5','PH6','PH7','PH8','PH9',
'PA1','PA10','PA11','PA12','PA14','PA3','PA4','PA5','PA6','PA7','PA8','PA9',
'EH26','EH38','EH43','EH44','EH45','EH46','ML12','TD1','TD10','TD11','TD12','TD13','TD14',
'TD15','TD2','TD3','TD4','TD5','TD6','TD7','TD8','TD9',
'ZE1','ZE2','ZE3','FK15','FK16','FK17','FK18','FK19','FK20','FK21','FK6','FK7','FK8','FK9','G63',
'EH27','EH30','EH47','EH48','EH49','EH52','EH53','EH54',
'EH55','HS1','HS2','HS3','HS4','HS5','HS6','HS7','HS8','HS9'
)

I know i cant use a 'IN' i should be using a 'like' or something I also thought maybe concatenate the postcode column and place in a temp table to run the query.

Any Idea on how i can run this would be very much appreciated. Thanks

Answer 1

Split this into 2 conditions:

WHERE left(Postcode, 3)  in (<constants with 3 characters>) or
      left(Postcode, 4) in (<constants with 4 characters>)

Or, create a table, say ScotlandPostPrefixes, with all the values. You can then use a join for the condition. You can even use an index to make this fast with the following trick:

from table t left outer join
     ScotlandPostPrefixes spp3
     on left(Postcode, 3) = spp3.Prefix left outer join
     ScotlandPostPrefixes spp4
     on left(Postcode, 4) = spp4.Prefix 
where spp3.Prefix is not null or spp4.Prefix is not null

This looks more complicated, but it will actually take advantage of an index on ScotlandPostPrefixes(Prefix) for processing.