Unexpected result w/ DISTINCT and variable concat

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Unexpected result w/ DISTINCT and variable concat

Author

Topic

ThreePea
Yak Posting Veteran

83 Posts

Posted - 2005-10-10 : 12:13:36

Hey everyone,

A co-op here at work just stumped me with the following:


USE Northwind
go
DECLARE @lastname_list VARCHAR(50)
SET @lastname_list = ''

SELECT 
  --DISTINCT
  @lastname_list = @lastname_list + E.LastName + ','
FROM Employees AS E 
WHERE E.EmployeeID IN (1,2)

SELECT @lastname_list

When you run this as-is, you get the expected result. However, if you uncomment the DISTINCT, you only get the first column in the variable. This surprised me. According to BOL, DISTINCT specifieds only unique rows can be in the result set; so I don't see how or why the query is stopped after the first row because it would still be unique if all the rows are processed.

(Yes, yes, I know the right answer is just "don't use the DISTINCT", but he asked me *why* and he thinks I know everything. I can't disappoint him.

)

Thanks.

3P

Kristen
Test

22859 Posts

Posted - 2005-10-10 : 12:25:53

You are preventing the assignment working as you intended using DISTINCT. What you would need to do is:


SELECT @lastname_list = @lastname_list + X.LastName + ','
FROM
(
    SELECT DISTINCT E.LastName
    FROM Employees AS E 
    WHERE E.EmployeeID IN (1,2)
) X

Kristen

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