Strange phenomenon with substring and charindex - sql

Question

When comparing the code snippets below, you can see that the last element of the 'result 1' result set, only has one character (a comma) appending the number, whereas the other numbers (rows 1 - 3) have a comma and a number appending the 4 digits that I want.
In the 'Result 2' result set, I specifically change the length of the substring to be the string length minus two characters, yet the last element only removes a single element, the trailing comma, while the rows 1 - 3 remove both the number and the trailing comma. There is no blank space in the last row. Please could someone advise why this is happening?
Code 1:
select substring(c,2,charindex(',',c,2)) as empno
from table t
where len(c) > 1
and substring(c,1,1) = ','
Result 1:
7654,7
7698,7
7782,7
7788,
Code 2:
select substring(c,2,charindex(',',c,2)-2) as empno
from table t
where len(c) > 1
and substring(c,1,1) = ','
Result 2:
7654
7698
7782
7788
*edit: table t is:-
c
----------------------
,7654,7698,7782,7788,
7654,7698,7782,7788,
654,7698,7782,7788,
54,7698,7782,7788,
4,7698,7782,7788,
,7698,7782,7788,
7698,7782,7788,
698,7782,7788,
98,7782,7788,
8,7782,7788,
,7782,7788,
7782,7788,
782,7788,
82,7788,
2,7788,
,7788,
7788,
788,
88,
8,
,

Answer 1

CHARINDEX:
Returns part of a character, binary, text, or image expression in SQL Server.
is defined as:
CHARINDEX ( expressionToFind , expressionToSearch [ , start_location ] )
AND
SUBSTRING:
Returns part of a character, binary, text, or image expression in SQL Server.
is defined as:
SUBSTRING ( expression ,start , length )
Query1:
substring(c,2,charindex(',',c,2))
In above charIndex returns first position of ',' i.e. 6 in every case.
So the returned value is acting as length for the substring which is 6 and that's why you are getting each record of 6 lengths.
Query 2:
substring(c,2,charindex(',',c,2)-2)
In above charIndex returns first position of ',' i.e. 6 in every case. But also you are reducing the length by subtracting 2 from it.
So the returned value is acting as length for the substring which is 4 now and that's why you are getting each record of 4 lengths in this query.
See this query1 and query2 represent CHARINDEX returned values:
c query1 query2
,7654,7698,7782,7788, 6 4
,7698,7782,7788, 6 4
,7782,7788, 6 4
,7788, 6 4