SQL sub query?

Question

SQL sub query?

bicky1980

SSCrazy

Points: 2079
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June 15, 2010 at 5:58 am

#225612

Hello All
I have a table which consists many records, which also have an additional flag
The data looks something like this
Postcode Flag
AB Y
AB
AB
AB Y
BL
BL Y
BL Y
What I want to do is query this table and return the following:
Postcode recordcount flagcount
AB 4 2
BL 3 2
Now at the moment I am getting these results by running 2 seperate queries, which I want to be able to perform in just 1 query. I have never done a sub query before so would like advise on how to build this statement
Thanks guys

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Adi Cohn-120898 SSC-Dedicated Points: 33944 More actions · Answer 1

You can use a case statement inside sum function to check if you need to count a record according to the value in the flag column. Here is an example:

use tempdb

go

create table Demo (PostCode char(2), flag char(1) null)

go

--Inserting the data

insert into Demo (PostCode, flag) values ('AB', null)

go 2

insert into Demo (PostCode, flag) values ('AB', 'Y')

go 2

insert into Demo (PostCode, flag) values ('BL', 'Y')

go 2

insert into Demo (PostCode, flag) values ('BL', NULL)

go

--First way. Using case to decide if the record should be counted

select PostCode, count(*) as NumOfRecords,

sum(CASE WHEN flag = 'Y' THEN 1 ELSE 0 END) as NumOfFlag

from Demo

group by PostCode

go

--Cleanup

drop table Demo

Adi

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ColdCoffee SSC-Dedicated Points: 39972 More actions · Answer 2

ColdCoffee

SSC-Dedicated

Points: 39972

June 15, 2010 at 6:18 am

#1180338

Ah, i was about to post the same code!

bicky1980 SSCrazy Points: 2079 More actions · Answer 3

Works a treat, thanks very much! This will save me lots of time...

prashant.bhatt SSC-Addicted Points: 476 More actions · Answer 4

You can also use the following query....

select PostCode, count(*) as NumOfRecords,

count(flag) as NumOfFlag

from Demo

group by PostCode

Prashant Bhatt
Sr Engineer - Application Programming

SQL sub query?

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