不与其他列一起使用

Question

I am trying to use distinct in my query

select distinct tvpAuditevent.TESTSEQUENCEID
from tvpAuditevent
where tvpAuditevent.Name = 'WorkstepCompleted';

it works fine. and give me only 100 Results

But now if I add other columns like this

select distinct tvpAuditevent.TESTSEQUENCEID, tvpAuditevent.USERNAME
from  tvpAuditevent
where tvpAuditevent.Name = 'WorkstepCompleted';

it gives me around 200 results, which is wrong. I need to only those 100 results but need other columns as well other than testsequenceId.

Please let me know if there is a way to do this.

Thanks

Answer 1

As explained in another answer, the distinct keyword applies to all the columns in the select statement. You cannot limit it to just one column.

Instead, you can use group by along with an aggregation function. For instance, the following returns the minimum value from the second column:

select ae.TESTSEQUENCEID, min(ae.USERNAME)
from  tvpAuditevent ae
where ae.Name = 'WorkstepCompleted'
group by ae.TESTSEQUENCEID;

In fact, the distinct keyword in a select is just a notational convenience. The following:

select distinct col1, col2, . . ., coln
from table t

does the same thing as:

select col1, col2, . . . coln
from table t
group by col1, col2, . . . coln

Answer 2

The keyword DISTINCT will simply remove duplicate results from the result set. It cannot be applied to a single column when you are selecting multiple columns.

What you want exactly is not clear. Let's say we have the following data, where the first value is the column you want to be distinct, and the other the column you want to display as "extra data".

A,B
A,C

What should the result be? A,B or A,C ?

Answer 3

SELECT S.TESTSEQUENCEID,
 AE.tvpAuditevent.USERNAME     
FROM tvpAuditevent AE
JOIN     (select distinct tvpAuditevent.TESTSEQUENCEID 
 from tvpAuditevent where tvpAuditevent.Name = 'WorkstepCompleted' ) S
 ON S.TESTSEQUENCEID = AE.TESTSEQUENCEID
where AE.tvpAuditevent.Name = 'WorkstepCompleted'