Conversion failed when converting the nvarchar

hello,
  I have two tables that I would like to join based on a column . However, the columns are different types. I get this error when I run the code 'Conversion failed when converting the nvarchar ' .

jobreference= (nvarchar(100),null)
job_code = int

Here is my query
select *  from DataJobs
LEFT JOIN posted_jobs 
ON jobreference= job_code

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I tried casting
select *  from DataJobs
LEFT JOIN posted_jobs 
ON jobreference= CAST(@job_code,nvarchar(100))

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but i get another error 'Must declare the scalar variable @job_code"
How do get this qry to work

Thanks
SiemensSENAsked:
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Jim HornMicrosoft SQL Server Developer, Architect, and AuthorCommented:
Lots of things to work on here...

(1) T-SQL needs to know what tables all JOIN columns are from, either  DataJobs.jobreference or posted_jobs.jobreference
(2)  Your JOIN only references one column, as the CAST includes a variable, so it effectively does not JOIN both tables.
  jobcode is a column (I'm guessing), and @jobcode is a variable.  Big difference.
(3)  CAST(something as nvarchar(100)), not CAST(something, nvarchar(100))
(4)  fyi SELECT * from a two-table join will return all columns in BOTH tables.  Verify that that's what you want.
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SimonCommented:
select *  from DataJobs
LEFT JOIN posted_jobs
ON convert(int,DataJobs.jobreference)= posted_jobs.job_code

This should work if the the datajobs table contains the jobreference column.
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SiemensSENAuthor Commented:
Thanks
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Jim HornMicrosoft SQL Server Developer, Architect, and AuthorCommented:
btw the answer you chose as the accepted solution will fail if any value in Datajobs.jobreference cannot be converted to an integer, e.g.
SELECT CONVERT(int, 'banana') 

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SimonCommented:
That's true. I was asssuming that the job reference is a varchar representation of a number. I find that I often make assumptions about what the OP is working with: I also made a guess as to which table contained each of the join columns. A trade-off between asking for more information and giving a quick answer that is likely, but not guaranteed to work.
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Jim HornMicrosoft SQL Server Developer, Architect, and AuthorCommented:
Fair enough.  There are a lot of problems with the asker's T-SQL, so I went the route of flushing out everything I saw.
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