Question

Good afternoon,

I am trying to use CASE like in this question to transpose rows to columns:

Rows to columns SQL Server query

However in my case I don’t have a column with information it’s a count of data.

I obtain the data with this query:

select MA, SN, count(*) 
from Original
where MA = 'AB'
group by MA

Result of the query:

MA  SN      COUNT
AB  TEXTA   6
AB  TEXTB   5
AB  TEXTC   3
AB  TEXTD   4

table Original

MA  SN      
AB  TEXTA   
AB  TEXTA   
AB  TEXTA   
AB  TEXTA   
AB  TEXTA   
AB  TEXTA   
.
.
.
AB  TEXTD   
AB  TEXTD   

table Result:

MA      TEXTA   TEXTB   TEXTC   TEXTD
AB      6       5       3       4

And this is my current query:

select  MA,
        count(*) as 'COUNT2',
    MAX(CASE WHEN SN = 'TEXTA' THEN COUNT2 end) as TEXTA1,
    MAX(CASE WHEN SN = 'TEXTB' THEN COUNT2 end) as TEXTB1,
    MAX(CASE WHEN SN = 'TEXTC' THEN COUNT2 end) as TEXTC1,
    MAX(CASE WHEN SN = 'TEXTD' THEN COUNT2 end) as TEXTD1,

from Original
where MA= 'AB'
group by MA

WHat am I doing horribly wrong in the query?. And can someone please explain why in the question I posted it works but not with the count?. Thank you! : ).

Answer 1

Edit: You can’t use COUNT2 in the way you intend because later columns in the select list cannot refer to aliases of previous columns. So COUNT2 has no meaning anywhere else in the query, unless you convert that part into a subquery (or cte) and then refer to it.

So, with your updated schema, it makes sense that you will need a subquery to do the counts. Essentially drop your first query as a subquery to the second query (in replace of Original), and then add a few missing group by columns, and then it works:

select  MA,
    MAX(CASE WHEN SN = 'TEXTA' THEN COUNT2 end) as TEXTA1,
    MAX(CASE WHEN SN = 'TEXTB' THEN COUNT2 end) as TEXTB1,
    MAX(CASE WHEN SN = 'TEXTC' THEN COUNT2 end) as TEXTC1,
    MAX(CASE WHEN SN = 'TEXTD' THEN COUNT2 end) as TEXTD1
from (
    select MA, SN, count(*) as COUNT2
    from Original
    where MA = 'AB'
    group by MA, SN
) Original
where MA= 'AB'
group by MA

http://www.sqlfiddle.com/#!3/41c79/7