Is there a rule for naming columns a certain name? - sql-server

Question

So we have a SQL Server 2017 instance with the default collation of Vietnamese_100_CI_AS_KS.
When we create a Temp Table, we see that if a specific name is used, it somehow sees one letter as case sensitive.
Example:
CREATE TABLE #MaterialTest
(
Product VARCHAR(50),
Quality VARCHAR (50),
MaterialOriginGroup VARCHAR (50)
)
INSERT INTO #MaterialTest VALUES ('Papers', 'Good', 'Test1')
If I query this table using:
Select Product, Quality, MaterialOriginGroup from #MaterialTest
It works fine. If I query it using pretty much anything else it works fine
But if I use a lower case "G" for "Group" in MaterialOriginGroup it fails.
Example:
Use TempDB
Select product, quality, materialorigingroup from #MaterialTest
Msg 207, Level 16, State 1, Line 2 Invalid column name
'materialorigingroup'.
If I query it with:
Use TempDB
Select product, quality, materialoriginGroup from #MaterialTest
It works.
Any idea why?

Answer 1

Building on my own investigations and #Larnu's SQL Fiddle, I've devised a little script to test two-letter combinations:
DECLARE #Letter VARCHAR(2);
SET #Letter = 'ch';
DECLARE #LetterA VARCHAR(1);
DECLARE #LetterB VARCHAR(1);
SET #LetterA = LEFT(#Letter, 1);
SET #LetterB = RIGHT(#Letter, 1);
SELECT CASE WHEN V.G = UPPER(#Letter) COLLATE Vietnamese_100_CI_AS_KS THEN 1 ELSE 0 END,
CASE WHEN V.G = LOWER(#Letter) COLLATE Vietnamese_100_CI_AS_KS THEN 1 ELSE 0 END,
CASE WHEN V.G = CONCAT(LOWER(#LetterA), UPPER(#LetterB)) COLLATE Vietnamese_100_CI_AS_KS THEN 1 ELSE 0 END,
CASE WHEN V.G = CONCAT(UPPER(#LetterA), LOWER(#LetterB)) COLLATE Vietnamese_100_CI_AS_KS THEN 1 ELSE 0 END
FROM (VALUES(#Letter COLLATE Vietnamese_100_CI_AS_KS)) V(G);
This will output 1 or 0 depending upon whether a comparison is valid for the two letter combination. The comparisons are:
Upper case letters (i.e. NG)
Lower case letters (i.e. ng)
One upper case, one lower case letter (i.e. Ng)
One lower case, one upper case letter (i.e. nG)
Running this for ab produces:
1 1 1 1
So ab does not exhibit this issue. However, for ch you get:
1 1 0 1
So ch does exhibit the same issue.
This seems related to declared consonants in the Vietnamese alphabet, which include these two-letter consonants:
Ch = 1 1 0 1 (has the same issue)
Gh = 1 1 0 1 (has the same issue)
Gi = 1 1 0 1 (has the same issue)
Kh = 1 1 0 1 (has the same issue)
Ng = 1 1 0 1 (has the same issue)
Nh = 1 1 0 1 (has the same issue)
Ph = 1 1 0 1 (has the same issue)
Qu = 1 1 0 1 (has the same issue)
Th = 1 1 0 1 (has the same issue)
Tr = 1 1 0 1 (has the same issue)
Unfortunately, I do not know why these are affected by this issue, which is not helpful. In addition, I don't know why it only affects the column name when it is a lowercase followed by an uppercase letter.
Perhaps someone else may see this and know the answer?
The reference for the alphabet is here.