why are the results of variable and condition are different? - sql

Question

I was wondering to figure out this problem.
In the below query am trying to select #transcript as the combination of 2 column values. but when i am using this variable in select statement am getting only 3 results (actual output should be 8 results). where as when i use the condition directly in select statement am getting actual output.
can anybody please help me in figuring out this issue.
declare #transcript varchar(10)
select #transcript = [CAREER_CD]+[CAREER_SUFX_CD] from dbo.SR0DAT
select DISTINCT #transcript transcriptCareerCode,
case #transcript
when 'U1' then 'BACCALAUREATE'
when 'U2' then 'SECOND BACCALAUREATE'
when 'G1' then 'GRADUATE'
when 'L1' then 'LAW'
when 'D1' then 'DENTISTRY'
when 'M1' then 'MEDICINE'
when 'IU' then 'transcriptCareerName'
when 'IG' then 'IEO Graduate'
end as transcriptCareerName
from dbo.SR0DAT
WHERE #transcript <>'G2'
union
select 'IU','IEO Undergraduate'
union
select 'IG','IEO Graduate'
output:
transcriptCareerCode transcriptCareerName
G1 GRADUATE
IG IEO Graduate
IU IEO Undergraduate
2nd code:
select DISTINCT [CAREER_CD]+[CAREER_SUFX_CD] transcriptCareerCode,
case [CAREER_CD]+[CAREER_SUFX_CD]
when 'U1' then 'BACCALAUREATE'
when 'U2' then 'SECOND BACCALAUREATE'
when 'G1' then 'GRADUATE'
when 'L1' then 'LAW'
when 'D1' then 'DENTISTRY'
when 'M1' then 'MEDICINE'
when 'IU' then 'transcriptCareerName'
when 'IG' then 'IEO Graduate'
end as transcriptCareerName
from dbo.SR0DAT
WHERE [CAREER_CD]+[CAREER_SUFX_CD] !='G2'
union
select 'IU','IEO Undergraduate'
union
select 'IG','IEO Graduate'
output:
transcriptCareerCode transcriptCareerName
D1 DENTISTRY
G1 GRADUATE
IG IEO Graduate
IU IEO Undergraduate
L1 LAW
M1 MEDICINE
U1 BACCALAUREATE
U2 SECOND BACCALAUREATE

Answer 1

While both queries are indeed run against your table none of its columns are being used at all in the first one: for each row you're simply returning a fixed/constant expression. The distinct option is helping to mask what's going on and if you remove the that you'll see all of the multiple copies that are being collapsed into one row. If you also say select #transcript, * ... you'll see where the rest of the data is as well.
Are you just trying to accomplish an alias for the transcript expression so you don't have to repeat it?
with T as (
select CAREER_CD + CAREER_SUFX_CD as transcript
from dbo.SR0DAT
)
select DISTINCT
transcript transcriptCareerCode,
case transcript
when 'U1' then 'BACCALAUREATE'
when 'U2' then 'SECOND BACCALAUREATE'
when 'G1' then 'GRADUATE'
when 'L1' then 'LAW'
when 'D1' then 'DENTISTRY'
when 'M1' then 'MEDICINE'
when 'IU' then 'transcriptCareerName'
when 'IG' then 'IEO Graduate'
end as transcriptCareerName
from T
where transcript <> 'G2'
union
select 'IU', 'IEO Undergraduate'
union
select 'IG', 'IEO Graduate'

Answer 2

In your first query you are creating a singular value through the variable #transcript. As a result, your call to:
select #transcript = [CAREER_CD]+[CAREER_SUFX_CD] from dbo.SR0DAT
Only guarantees that the last record in the SELECT statement gets assigned to the #transcript variable.
As a result, only one row from that query will return (you've union'ed the other two rows in your first example).
The second example is using actual database set logic to pull in values across the set - not just the last value in the set.