not able to identify difference between same value - sql-server

Question

I have data inside a table's column. I SELECT DISTINCT of that column, i also put LTRIM(RTRIM(col_name)) as well while writing SELECT. But still I am getting duplicate column record.
How can we identify why it is happening and how we can avoid it?
I tried RTRIM, LTRIM, UPPER function. Still no help.
Query:
select distinct LTRIM(RTRIM(serverstatus))
from SQLInventory
Output:
Development
Staging
Test
Pre-Production
UNKNOWN
NULL
Need to be decommissioned
Production
Pre-Produc​tion
Decommissioned
Non-Production
Unsupported Edition

Answer 1

Looks like there's a unicode character in there, somewhere. I copied and pasted the values out initially as a varchar, and did the following:
SELECT DISTINCT serverstatus
FROM (VALUES('Development'),
('Staging'),
('Test'),
('Pre-Production'),
('UNKNOWN'),
('NULL'),
('Need to be decommissioned'),
('Production'),
(''),
('Pre-Produc​tion'),
('Decommissioned'),
('Non-Production'),
('Unsupported Edition'))V(serverstatus);
This, interestingly, returned the values below:
Development
Staging
Test
Pre-Production
UNKNOWN
NULL
Need to be decommissioned
Production
Pre-Produc?tion
Decommissioned
Non-Production
Unsupported Edition
Note that one of the values is Pre-Produc?tion, meaning that there is a unicode character between the c and t.
So, let's find out what it is:
SELECT 'Pre-Produc​tion', N'Pre-Produc​tion',
UNICODE(SUBSTRING(N'Pre-Produc​tion',11,1));
The UNICODE function returns back 8203, which is a zero-width space. I assume you want to remove these, so you can update your data by doing:
UPDATE SQLInventory
SET serverstatus = REPLACE(serverstatus, NCHAR(8203), N'');
Now your first query should work as you expect.
(I also suggest you might therefore want a lookup table for your status' with a foreign key, so that this can't happen again).
DB<>fiddle

Answer 2

I deal with this type of thing all the time. For stuff like this NGrams8K and PatReplace8k and PATINDEX are your best friends.
Putting what you posted in a table variable we can analyze the problem:
DECLARE #table TABLE (txtID INT IDENTITY, txt NVARCHAR(100));
INSERT #table (txt)
VALUES ('Development'),('Staging'),('Test'),('Pre-Production'),('UNKNOWN'),(NULL),
('Need to be decommissioned'),('Production'),(''),('Pre-Produc​tion'),('Decommissioned'),
('Non-Production'),('Unsupported Edition');
This query will identify items with characters other than A-Z, spaces and hyphens:
SELECT t.txtID, t.txt
FROM #table AS t
WHERE PATINDEX('%[^a-zA-Z -]%',t.txt) > 0;
This returns:
txtID txt
----------- -------------------------------------------
10 Pre-Produc​tion
To identify the bad character we can use NGrams8k like this:
SELECT t.txtID, t.txt, ng.position, ng.token -- ,UNICODE(ng.token)
FROM #table AS t
CROSS APPLY dbo.NGrams8K(t.txt,1) AS ng
WHERE PATINDEX('%[^a-zA-Z -]%',ng.token)>0;
Which returns:
txtID txt position token
------ ----------------- -------------------- ---------
10 Pre-Produc​tion 11 ?
PatReplace8K makes cleaning up stuff like this quite easily and quickly. First note this query:
SELECT OldString = t.txt, p.NewString
FROM #table AS t
CROSS APPLY dbo.patReplace8K(t.txt,'%[^a-zA-Z -]%','') AS p
WHERE PATINDEX('%[^a-zA-Z -]%',t.txt) > 0;
Which returns this on my system:
OldString NewString
------------------ ----------------
Pre-Produc?tion Pre-Production
To fix the problem you can use patreplace8K like this:
UPDATE t
SET txt = p.newString
FROM #table AS t
CROSS APPLY dbo.patReplace8K(t.txt,'%[^a-zA-Z -]%','') AS p
WHERE PATINDEX('%[^a-zA-Z -]%',t.txt) > 0;