Joining part of a field to another table

Posted on 2007-04-03
Last Modified: 2010-03-19
Dear Experts

I have two tables

Document_Filename (i.e. nick.gif)


How can I extract the extension description from FileTypes (FileType_Description) from Document_Filename (where available)

I'm looking for the following result from my query:

Document_Filename  |  TypeOfFile
nick.gif                        CompuServe GIF

Any help would be appreciated

Question by:nkewney
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LVL 50

Expert Comment

ID: 18847479
which database system the sql syntax varies...
obviously you should hold the filetype as a distinct column in your table and then this would be unnecessary...
LVL 50

Accepted Solution

Lowfatspread earned 500 total points
ID: 18847507
you could try ,..

select document_filename
    ,case when filetype_description is null then 'Unknown fileType'
                 else filetype_description end as typeoffile
 from documents as d
 left outer join filetypes as ft
  on d.document_filename + ' ' like '%.' + + ' %'  
LVL 11

Expert Comment

ID: 18847514

You can use this function to extract file extension:
It returns substring after the last . (dot)

I hope this can help you

Best Regards
LVL 11

Expert Comment

ID: 18847525
When i use Your code and use filename sth.gif.whatever.exe i can get wrong result

Correct me if im wrong.
LVL 11

Expert Comment

ID: 18847560
If you are sure there is always just one '.' in the Document_Filename, you could use sqls substr and charindex functions.

SELECT SUBSTR(Document_Filename, charindex('.', Document_Filename))  from documents

should give  you the extension. If it has the . with it, you have to add a + 1 after the charindex.

The join could probably be done like:
SELECT documents.Document_Filename, FileTypes.FileType_Description from
documents left join FileTypes on FileTypes.FileType_Name = SUBSTR(Document_Filename, charindex('.', Document_Filename))

not sure, but give it a try

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