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I am working with the "Joins" option in QGIS 3.10, which joins the fields from two attribute tables based on a common shared attribute column.

However, this does not work for attribute values with a large length.

E.g. the following field value can be joined: 2404252385

While this one cannot: 551482643342511892418838370

I checked carefully if it may be due to other problems, but it clearly seems to be the problem of the number of characters. For example, I can filter both features by the attribute fields, which returns the respective row. However, the joined fields nevertheless show 'NULL', i.e. the common field name could not be found.

Can somebody confirm this problem and is there maybe a workaround/solution to fix this?

Edit: I am referring to field values, not field names. I tested around and possible issues that might be the problem are:

  • The columns that I want to join are both called "fid"
  • The columns that I want to join are of type string, not integer
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    Please Edit the question to clarify if "2404252385" and "551482643342511892418838370" are field names or field values. If they're names, you really ought to prefix them with a character (a-z), so that they're legal names. – Vince Feb 17 at 19:05
  • Fixed this to refer to field values. I also edited the post, to provide more information what I found out could be an issue – LeonardH Feb 18 at 9:51
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Fieldnames of shapefiles are limited to 10 characters. You can use another file-format like Geopackage to bypass this issue.

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    Will geopackage support all-numeric column names? – Vince Feb 17 at 19:06
  • Valid question. I am not sure about official specifications, but did a quick test and its working fine. However need to figure this out at docs. – MrXsquared Feb 17 at 21:14
  • Trying to use the Geopackage file format did not resolve the issue, but then it was also meant to bypass the issue of fieldname character size. I clarified above that I have the problem specifically due to the fieldvalue character size. – LeonardH Feb 19 at 9:56
  • It was about how I originally understood your question, so about length of fieldnames. But you can also use longer fieldvalues in geopackage than in shapefiles. How did you specify the field? Name, Type and length of its content? – MrXsquared Feb 19 at 10:09
  • The long (27-character size) fieldvalues are also displayed in the shapefile-format. The fieldname is 'fid', the type is QString/string, and the length is 50 – LeonardH Feb 20 at 10:37

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