SQL Server 2008 R2 bug or what? - sql-server

Question

I am observing a strange behaviour. The following code that is related to conversion of a substring of nvarchar to tinyint works fine:
DECLARE #s nvarchar(50) = N'Line 1'
DECLARE #n tinyint = SUBSTRING(#s, 6, 10)
SELECT
N'Line 1' AS explicit_nvarchar,
#s AS nvarchar_variable,
SUBSTRING(#s, 6, 10) AS nvarchar_substring
, #n AS tinyint_var_converted_earlier
, CAST(SUBSTRING(#s, 6, 10) AS tinyint) AS cast_sub_var
, CAST(SUBSTRING(N'Line 1', 6, 10) AS tinyint) AS cast_nvarchar_substr
I can observe the following output in the Microsoft SQL Server Management Studio:
.
However, the code that tries to do with the SELECT from the tables fails if the commented line is uncommented:
Select
[order].[identifier] As [order_identifier],
[plan_data].[starts_on] As [from],
[plan_data].[ends_on] As [to],
[workplace].[identifier] AS line_identifier,
SUBSTRING([workplace].[identifier], 6, 10) AS line_no_str
--, CAST(SUBSTRING([workplace].[identifier], 6, 10) AS int) AS line_no
From
...
With commented line...
but with uncommented line (both for conversion to tinyint or int)...
Update: Strange. I have added the last line to the WHERE to check whether all lines
contain the 'Line...
Where
[plan].[identifier] = #lPlanIdentifier And
(
[plan_data].[starts_on] Between #fromUTC And #toUTC Or
[plan_data].[ends_on] Between #fromUTC And #toUTC)
AND LEFT([workplace].[identifier], 4) = N'Line'
... and all of a sudden it works also with the uncommented line. How can I discover what causes the problem?
Update2: I should have followed the Hamlet Hakobyan's answer exactly as it was published. When looking inside the table, I can see:

Answer 1

You have value in identifier column for which SUBSTRING([workplace].[identifier], 6, 10) returns ined.
Try this query:
SELECT * FROM [workplace]
WHERE SUBSTRING([identifier], 6, 10) = N'ined'

Answer 2

As indicated by the comments and other answer(s), you have a value in [workplace].[identifier] for one or more rows that fails to cast to an INT. When you added the following to the WHERE clause, you eliminated the row(s) that has this data before it was converted in the SELECT clause:
LEFT([workplace].[identifier], 4) = N'Line'
Run the following to get a distinct list of values in [workplace].[identifier]
SELECT DISTINCT [workplace].[identifier]
FROM [workplace]

Answer 3

Whenever you have an error converting a varchar to a number the easiest way to find the data is using IsNumeric. However IsNumeric doesn't mean IsInteger so its worth removing scientific or decimal formats as described by G Mastros in this answer
SELECT
[order].[identifier] As [order_identifier],
[plan_data].[starts_on] As [from],
[plan_data].[ends_on] As [to],
[workplace].[identifier] AS line_identifier,
SUBSTRING([workplace].[identifier], 6, 10) AS line_no_str
--, CAST(SUBSTRING([workplace].[identifier], 6, 10) AS int) AS line_no
FROM
...
WHERE
IsNumeric(SUBSTRING([workplace].[identifier], 6, 10) + '.0e0') = 0
If you can't fix it but you can use a default value than you could use a case statement to do the conversion only when its legal to do so.
SELECT
[order].[identifier] As [order_identifier],
[plan_data].[starts_on] As [from],
[plan_data].[ends_on] As [to],
[workplace].[identifier] AS line_identifier,
CASE WHEN IsNumeric(SUBSTRING([workplace].[identifier], 6, 10) + '.0e0') = 1
THEN CAST(SUBSTRING([workplace].[identifier], 6, 10) AS int)
ELSE Null --Default to null in this example
END as line_no