Question

I have a sample data as:

Johnson; Michael, Surendir;Mishra, Mohan; Ram
Johnson; Michael R.
Mohan; Anaha
Jordan; Michael
Maru; Tushar

The output of the query should be:

Johnson; Michael   2
Mohan; Anaha       1
Michael; Jordon    1
Maru; Tushar       1
Surendir;Mishra    1
Mohan; Ram         1

As you can see it is print the count of each name separated by , but with a twist. We cannot simply do a groupby on full name because sometimes the name may contain middle name 1st initial and sometimes it may not. Eg. Johnson; Michael and Johnson; Michael R. are counted as single name and hence their count is 2. Further either Johnson; Michael should appear or Johnson; Michael R. should appear in resultset with count of 2 (not both because that would be repeated record)

The table contains names separated by , and it is not possible to denormalize it as it is LIVE and given to us by someone else.

Is there anyway to write a query for this without using cursor? I have around 3 million records in my DB and I have to support pagination etc also. What do you think would be the best way to achieve this?

Answer 1

This is why your data should be normalised.

;with cte as  
( 
    select 1 as Item, 1 as Start, CHARINDEX(',',People+',' , 1) as Split, 
           People+',' as People 
    from YourHorribleTable
    union all 
    select cte.Item+1, cte.Split+1, nullif(CHARINDEX(',',people, cte.Split+1),0), People as Split 
    from cte 
    where cte.Split<>0   
)    
select Person, COUNT(*)
from
(
select case when nullif(charindex (' ', person, 2+nullif(CHARINDEX(';', person),0)),0) is null then person  
    else substring(person,1,charindex (' ', person, 2+nullif(CHARINDEX(';', person),0)))
    end as Person
from
(
select LTRIM(RTRIM( SUBSTRING(people, start,isnull(split,len(People)+1)-start))) as person
from cte  
) v
where person<>''
) v
group by Person
order by COUNT(*) desc